[www-releases] r246586 - Commit 3.7.0

Hans Wennborg via llvm-commits llvm-commits at lists.llvm.org
Tue Sep 1 13:55:36 PDT 2015


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URL: http://llvm.org/viewvc/llvm-project/www-releases/trunk/3.7.0/docs/tutorial/LangImpl4.html?rev=246586&view=auto
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+  <div class="section" id="kaleidoscope-adding-jit-and-optimizer-support">
+<h1>4. Kaleidoscope: Adding JIT and Optimizer Support<a class="headerlink" href="#kaleidoscope-adding-jit-and-optimizer-support" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#chapter-4-introduction" id="id1">Chapter 4 Introduction</a></li>
+<li><a class="reference internal" href="#trivial-constant-folding" id="id2">Trivial Constant Folding</a></li>
+<li><a class="reference internal" href="#llvm-optimization-passes" id="id3">LLVM Optimization Passes</a></li>
+<li><a class="reference internal" href="#adding-a-jit-compiler" id="id4">Adding a JIT Compiler</a></li>
+<li><a class="reference internal" href="#full-code-listing" id="id5">Full Code Listing</a></li>
+</ul>
+</div>
+<div class="section" id="chapter-4-introduction">
+<h2><a class="toc-backref" href="#id1">4.1. Chapter 4 Introduction</a><a class="headerlink" href="#chapter-4-introduction" title="Permalink to this headline">¶</a></h2>
+<p>Welcome to Chapter 4 of the “<a class="reference external" href="index.html">Implementing a language with
+LLVM</a>” tutorial. Chapters 1-3 described the implementation
+of a simple language and added support for generating LLVM IR. This
+chapter describes two new techniques: adding optimizer support to your
+language, and adding JIT compiler support. These additions will
+demonstrate how to get nice, efficient code for the Kaleidoscope
+language.</p>
+</div>
+<div class="section" id="trivial-constant-folding">
+<h2><a class="toc-backref" href="#id2">4.2. Trivial Constant Folding</a><a class="headerlink" href="#trivial-constant-folding" title="Permalink to this headline">¶</a></h2>
+<p>Our demonstration for Chapter 3 is elegant and easy to extend.
+Unfortunately, it does not produce wonderful code. The IRBuilder,
+however, does give us obvious optimizations when compiling simple code:</p>
+<div class="highlight-python"><div class="highlight"><pre>ready> def test(x) 1+2+x;
+Read function definition:
+define double @test(double %x) {
+entry:
+        %addtmp = fadd double 3.000000e+00, %x
+        ret double %addtmp
+}
+</pre></div>
+</div>
+<p>This code is not a literal transcription of the AST built by parsing the
+input. That would be:</p>
+<div class="highlight-python"><div class="highlight"><pre>ready> def test(x) 1+2+x;
+Read function definition:
+define double @test(double %x) {
+entry:
+        %addtmp = fadd double 2.000000e+00, 1.000000e+00
+        %addtmp1 = fadd double %addtmp, %x
+        ret double %addtmp1
+}
+</pre></div>
+</div>
+<p>Constant folding, as seen above, in particular, is a very common and
+very important optimization: so much so that many language implementors
+implement constant folding support in their AST representation.</p>
+<p>With LLVM, you don’t need this support in the AST. Since all calls to
+build LLVM IR go through the LLVM IR builder, the builder itself checked
+to see if there was a constant folding opportunity when you call it. If
+so, it just does the constant fold and return the constant instead of
+creating an instruction.</p>
+<p>Well, that was easy :). In practice, we recommend always using
+<tt class="docutils literal"><span class="pre">IRBuilder</span></tt> when generating code like this. It has no “syntactic
+overhead” for its use (you don’t have to uglify your compiler with
+constant checks everywhere) and it can dramatically reduce the amount of
+LLVM IR that is generated in some cases (particular for languages with a
+macro preprocessor or that use a lot of constants).</p>
+<p>On the other hand, the <tt class="docutils literal"><span class="pre">IRBuilder</span></tt> is limited by the fact that it does
+all of its analysis inline with the code as it is built. If you take a
+slightly more complex example:</p>
+<div class="highlight-python"><div class="highlight"><pre>ready> def test(x) (1+2+x)*(x+(1+2));
+ready> Read function definition:
+define double @test(double %x) {
+entry:
+        %addtmp = fadd double 3.000000e+00, %x
+        %addtmp1 = fadd double %x, 3.000000e+00
+        %multmp = fmul double %addtmp, %addtmp1
+        ret double %multmp
+}
+</pre></div>
+</div>
+<p>In this case, the LHS and RHS of the multiplication are the same value.
+We’d really like to see this generate “<tt class="docutils literal"><span class="pre">tmp</span> <span class="pre">=</span> <span class="pre">x+3;</span> <span class="pre">result</span> <span class="pre">=</span> <span class="pre">tmp*tmp;</span></tt>”
+instead of computing “<tt class="docutils literal"><span class="pre">x+3</span></tt>” twice.</p>
+<p>Unfortunately, no amount of local analysis will be able to detect and
+correct this. This requires two transformations: reassociation of
+expressions (to make the add’s lexically identical) and Common
+Subexpression Elimination (CSE) to delete the redundant add instruction.
+Fortunately, LLVM provides a broad range of optimizations that you can
+use, in the form of “passes”.</p>
+</div>
+<div class="section" id="llvm-optimization-passes">
+<h2><a class="toc-backref" href="#id3">4.3. LLVM Optimization Passes</a><a class="headerlink" href="#llvm-optimization-passes" title="Permalink to this headline">¶</a></h2>
+<p>LLVM provides many optimization passes, which do many different sorts of
+things and have different tradeoffs. Unlike other systems, LLVM doesn’t
+hold to the mistaken notion that one set of optimizations is right for
+all languages and for all situations. LLVM allows a compiler implementor
+to make complete decisions about what optimizations to use, in which
+order, and in what situation.</p>
+<p>As a concrete example, LLVM supports both “whole module” passes, which
+look across as large of body of code as they can (often a whole file,
+but if run at link time, this can be a substantial portion of the whole
+program). It also supports and includes “per-function” passes which just
+operate on a single function at a time, without looking at other
+functions. For more information on passes and how they are run, see the
+<a class="reference external" href="../WritingAnLLVMPass.html">How to Write a Pass</a> document and the
+<a class="reference external" href="../Passes.html">List of LLVM Passes</a>.</p>
+<p>For Kaleidoscope, we are currently generating functions on the fly, one
+at a time, as the user types them in. We aren’t shooting for the
+ultimate optimization experience in this setting, but we also want to
+catch the easy and quick stuff where possible. As such, we will choose
+to run a few per-function optimizations as the user types the function
+in. If we wanted to make a “static Kaleidoscope compiler”, we would use
+exactly the code we have now, except that we would defer running the
+optimizer until the entire file has been parsed.</p>
+<p>In order to get per-function optimizations going, we need to set up a
+<a class="reference external" href="../WritingAnLLVMPass.html#passmanager">FunctionPassManager</a> to hold
+and organize the LLVM optimizations that we want to run. Once we have
+that, we can add a set of optimizations to run. The code looks like
+this:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">FunctionPassManager</span> <span class="nf">OurFPM</span><span class="p">(</span><span class="n">TheModule</span><span class="p">);</span>
+
+<span class="c1">// Set up the optimizer pipeline.  Start with registering info about how the</span>
+<span class="c1">// target lays out data structures.</span>
+<span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="k">new</span> <span class="n">DataLayout</span><span class="p">(</span><span class="o">*</span><span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">getDataLayout</span><span class="p">()));</span>
+<span class="c1">// Provide basic AliasAnalysis support for GVN.</span>
+<span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createBasicAliasAnalysisPass</span><span class="p">());</span>
+<span class="c1">// Do simple "peephole" optimizations and bit-twiddling optzns.</span>
+<span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createInstructionCombiningPass</span><span class="p">());</span>
+<span class="c1">// Reassociate expressions.</span>
+<span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createReassociatePass</span><span class="p">());</span>
+<span class="c1">// Eliminate Common SubExpressions.</span>
+<span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createGVNPass</span><span class="p">());</span>
+<span class="c1">// Simplify the control flow graph (deleting unreachable blocks, etc).</span>
+<span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createCFGSimplificationPass</span><span class="p">());</span>
+
+<span class="n">OurFPM</span><span class="p">.</span><span class="n">doInitialization</span><span class="p">();</span>
+
+<span class="c1">// Set the global so the code gen can use this.</span>
+<span class="n">TheFPM</span> <span class="o">=</span> <span class="o">&</span><span class="n">OurFPM</span><span class="p">;</span>
+
+<span class="c1">// Run the main "interpreter loop" now.</span>
+<span class="n">MainLoop</span><span class="p">();</span>
+</pre></div>
+</div>
+<p>This code defines a <tt class="docutils literal"><span class="pre">FunctionPassManager</span></tt>, “<tt class="docutils literal"><span class="pre">OurFPM</span></tt>”. It requires a
+pointer to the <tt class="docutils literal"><span class="pre">Module</span></tt> to construct itself. Once it is set up, we use
+a series of “add” calls to add a bunch of LLVM passes. The first pass is
+basically boilerplate, it adds a pass so that later optimizations know
+how the data structures in the program are laid out. The
+“<tt class="docutils literal"><span class="pre">TheExecutionEngine</span></tt>” variable is related to the JIT, which we will
+get to in the next section.</p>
+<p>In this case, we choose to add 4 optimization passes. The passes we
+chose here are a pretty standard set of “cleanup” optimizations that are
+useful for a wide variety of code. I won’t delve into what they do but,
+believe me, they are a good starting place :).</p>
+<p>Once the PassManager is set up, we need to make use of it. We do this by
+running it after our newly created function is constructed (in
+<tt class="docutils literal"><span class="pre">FunctionAST::Codegen</span></tt>), but before it is returned to the client:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">if</span> <span class="p">(</span><span class="n">Value</span> <span class="o">*</span><span class="n">RetVal</span> <span class="o">=</span> <span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+  <span class="c1">// Finish off the function.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateRet</span><span class="p">(</span><span class="n">RetVal</span><span class="p">);</span>
+
+  <span class="c1">// Validate the generated code, checking for consistency.</span>
+  <span class="n">verifyFunction</span><span class="p">(</span><span class="o">*</span><span class="n">TheFunction</span><span class="p">);</span>
+
+  <span class="c1">// Optimize the function.</span>
+  <span class="n">TheFPM</span><span class="o">-></span><span class="n">run</span><span class="p">(</span><span class="o">*</span><span class="n">TheFunction</span><span class="p">);</span>
+
+  <span class="k">return</span> <span class="n">TheFunction</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>As you can see, this is pretty straightforward. The
+<tt class="docutils literal"><span class="pre">FunctionPassManager</span></tt> optimizes and updates the LLVM Function* in
+place, improving (hopefully) its body. With this in place, we can try
+our test above again:</p>
+<div class="highlight-python"><div class="highlight"><pre>ready> def test(x) (1+2+x)*(x+(1+2));
+ready> Read function definition:
+define double @test(double %x) {
+entry:
+        %addtmp = fadd double %x, 3.000000e+00
+        %multmp = fmul double %addtmp, %addtmp
+        ret double %multmp
+}
+</pre></div>
+</div>
+<p>As expected, we now get our nicely optimized code, saving a floating
+point add instruction from every execution of this function.</p>
+<p>LLVM provides a wide variety of optimizations that can be used in
+certain circumstances. Some <a class="reference external" href="../Passes.html">documentation about the various
+passes</a> is available, but it isn’t very complete.
+Another good source of ideas can come from looking at the passes that
+<tt class="docutils literal"><span class="pre">Clang</span></tt> runs to get started. The “<tt class="docutils literal"><span class="pre">opt</span></tt>” tool allows you to
+experiment with passes from the command line, so you can see if they do
+anything.</p>
+<p>Now that we have reasonable code coming out of our front-end, lets talk
+about executing it!</p>
+</div>
+<div class="section" id="adding-a-jit-compiler">
+<h2><a class="toc-backref" href="#id4">4.4. Adding a JIT Compiler</a><a class="headerlink" href="#adding-a-jit-compiler" title="Permalink to this headline">¶</a></h2>
+<p>Code that is available in LLVM IR can have a wide variety of tools
+applied to it. For example, you can run optimizations on it (as we did
+above), you can dump it out in textual or binary forms, you can compile
+the code to an assembly file (.s) for some target, or you can JIT
+compile it. The nice thing about the LLVM IR representation is that it
+is the “common currency” between many different parts of the compiler.</p>
+<p>In this section, we’ll add JIT compiler support to our interpreter. The
+basic idea that we want for Kaleidoscope is to have the user enter
+function bodies as they do now, but immediately evaluate the top-level
+expressions they type in. For example, if they type in “1 + 2;”, we
+should evaluate and print out 3. If they define a function, they should
+be able to call it from the command line.</p>
+<p>In order to do this, we first declare and initialize the JIT. This is
+done by adding a global variable and a call in <tt class="docutils literal"><span class="pre">main</span></tt>:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">static</span> <span class="n">ExecutionEngine</span> <span class="o">*</span><span class="n">TheExecutionEngine</span><span class="p">;</span>
+<span class="p">...</span>
+<span class="kt">int</span> <span class="n">main</span><span class="p">()</span> <span class="p">{</span>
+  <span class="p">..</span>
+  <span class="c1">// Create the JIT.  This takes ownership of the module.</span>
+  <span class="n">TheExecutionEngine</span> <span class="o">=</span> <span class="n">EngineBuilder</span><span class="p">(</span><span class="n">TheModule</span><span class="p">).</span><span class="n">create</span><span class="p">();</span>
+  <span class="p">..</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>This creates an abstract “Execution Engine” which can be either a JIT
+compiler or the LLVM interpreter. LLVM will automatically pick a JIT
+compiler for you if one is available for your platform, otherwise it
+will fall back to the interpreter.</p>
+<p>Once the <tt class="docutils literal"><span class="pre">ExecutionEngine</span></tt> is created, the JIT is ready to be used.
+There are a variety of APIs that are useful, but the simplest one is the
+“<tt class="docutils literal"><span class="pre">getPointerToFunction(F)</span></tt>” method. This method JIT compiles the
+specified LLVM Function and returns a function pointer to the generated
+machine code. In our case, this means that we can change the code that
+parses a top-level expression to look like this:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleTopLevelExpression</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Evaluate a top-level expression into an anonymous function.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">FunctionAST</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">ParseTopLevelExpr</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">LF</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">LF</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>  <span class="c1">// Dump the function for exposition purposes.</span>
+
+      <span class="c1">// JIT the function, returning a function pointer.</span>
+      <span class="kt">void</span> <span class="o">*</span><span class="n">FPtr</span> <span class="o">=</span> <span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">getPointerToFunction</span><span class="p">(</span><span class="n">LF</span><span class="p">);</span>
+
+      <span class="c1">// Cast it to the right type (takes no arguments, returns a double) so we</span>
+      <span class="c1">// can call it as a native function.</span>
+      <span class="kt">double</span> <span class="p">(</span><span class="o">*</span><span class="n">FP</span><span class="p">)()</span> <span class="o">=</span> <span class="p">(</span><span class="kt">double</span> <span class="p">(</span><span class="o">*</span><span class="p">)())(</span><span class="kt">intptr_t</span><span class="p">)</span><span class="n">FPtr</span><span class="p">;</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Evaluated to %f</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">FP</span><span class="p">());</span>
+    <span class="p">}</span>
+</pre></div>
+</div>
+<p>Recall that we compile top-level expressions into a self-contained LLVM
+function that takes no arguments and returns the computed double.
+Because the LLVM JIT compiler matches the native platform ABI, this
+means that you can just cast the result pointer to a function pointer of
+that type and call it directly. This means, there is no difference
+between JIT compiled code and native machine code that is statically
+linked into your application.</p>
+<p>With just these two changes, lets see how Kaleidoscope works now!</p>
+<div class="highlight-python"><div class="highlight"><pre>ready> 4+5;
+Read top-level expression:
+define double @0() {
+entry:
+  ret double 9.000000e+00
+}
+
+Evaluated to 9.000000
+</pre></div>
+</div>
+<p>Well this looks like it is basically working. The dump of the function
+shows the “no argument function that always returns double” that we
+synthesize for each top-level expression that is typed in. This
+demonstrates very basic functionality, but can we do more?</p>
+<div class="highlight-python"><div class="highlight"><pre>ready> def testfunc(x y) x + y*2;
+Read function definition:
+define double @testfunc(double %x, double %y) {
+entry:
+  %multmp = fmul double %y, 2.000000e+00
+  %addtmp = fadd double %multmp, %x
+  ret double %addtmp
+}
+
+ready> testfunc(4, 10);
+Read top-level expression:
+define double @1() {
+entry:
+  %calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01)
+  ret double %calltmp
+}
+
+Evaluated to 24.000000
+</pre></div>
+</div>
+<p>This illustrates that we can now call user code, but there is something
+a bit subtle going on here. Note that we only invoke the JIT on the
+anonymous functions that <em>call testfunc</em>, but we never invoked it on
+<em>testfunc</em> itself. What actually happened here is that the JIT scanned
+for all non-JIT’d functions transitively called from the anonymous
+function and compiled all of them before returning from
+<tt class="docutils literal"><span class="pre">getPointerToFunction()</span></tt>.</p>
+<p>The JIT provides a number of other more advanced interfaces for things
+like freeing allocated machine code, rejit’ing functions to update them,
+etc. However, even with this simple code, we get some surprisingly
+powerful capabilities - check this out (I removed the dump of the
+anonymous functions, you should get the idea by now :) :</p>
+<div class="highlight-python"><div class="highlight"><pre>ready> extern sin(x);
+Read extern:
+declare double @sin(double)
+
+ready> extern cos(x);
+Read extern:
+declare double @cos(double)
+
+ready> sin(1.0);
+Read top-level expression:
+define double @2() {
+entry:
+  ret double 0x3FEAED548F090CEE
+}
+
+Evaluated to 0.841471
+
+ready> def foo(x) sin(x)*sin(x) + cos(x)*cos(x);
+Read function definition:
+define double @foo(double %x) {
+entry:
+  %calltmp = call double @sin(double %x)
+  %multmp = fmul double %calltmp, %calltmp
+  %calltmp2 = call double @cos(double %x)
+  %multmp4 = fmul double %calltmp2, %calltmp2
+  %addtmp = fadd double %multmp, %multmp4
+  ret double %addtmp
+}
+
+ready> foo(4.0);
+Read top-level expression:
+define double @3() {
+entry:
+  %calltmp = call double @foo(double 4.000000e+00)
+  ret double %calltmp
+}
+
+Evaluated to 1.000000
+</pre></div>
+</div>
+<p>Whoa, how does the JIT know about sin and cos? The answer is
+surprisingly simple: in this example, the JIT started execution of a
+function and got to a function call. It realized that the function was
+not yet JIT compiled and invoked the standard set of routines to resolve
+the function. In this case, there is no body defined for the function,
+so the JIT ended up calling “<tt class="docutils literal"><span class="pre">dlsym("sin")</span></tt>” on the Kaleidoscope
+process itself. Since “<tt class="docutils literal"><span class="pre">sin</span></tt>” is defined within the JIT’s address
+space, it simply patches up calls in the module to call the libm version
+of <tt class="docutils literal"><span class="pre">sin</span></tt> directly.</p>
+<p>The LLVM JIT provides a number of interfaces (look in the
+<tt class="docutils literal"><span class="pre">ExecutionEngine.h</span></tt> file) for controlling how unknown functions get
+resolved. It allows you to establish explicit mappings between IR
+objects and addresses (useful for LLVM global variables that you want to
+map to static tables, for example), allows you to dynamically decide on
+the fly based on the function name, and even allows you to have the JIT
+compile functions lazily the first time they’re called.</p>
+<p>One interesting application of this is that we can now extend the
+language by writing arbitrary C++ code to implement operations. For
+example, if we add:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// putchard - putchar that takes a double and returns 0.</span>
+<span class="k">extern</span> <span class="s">"C"</span>
+<span class="kt">double</span> <span class="n">putchard</span><span class="p">(</span><span class="kt">double</span> <span class="n">X</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">putchar</span><span class="p">((</span><span class="kt">char</span><span class="p">)</span><span class="n">X</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Now we can produce simple output to the console by using things like:
+“<tt class="docutils literal"><span class="pre">extern</span> <span class="pre">putchard(x);</span> <span class="pre">putchard(120);</span></tt>”, which prints a lowercase ‘x’
+on the console (120 is the ASCII code for ‘x’). Similar code could be
+used to implement file I/O, console input, and many other capabilities
+in Kaleidoscope.</p>
+<p>This completes the JIT and optimizer chapter of the Kaleidoscope
+tutorial. At this point, we can compile a non-Turing-complete
+programming language, optimize and JIT compile it in a user-driven way.
+Next up we’ll look into <a class="reference external" href="LangImpl5.html">extending the language with control flow
+constructs</a>, tackling some interesting LLVM IR issues
+along the way.</p>
+</div>
+<div class="section" id="full-code-listing">
+<h2><a class="toc-backref" href="#id5">4.5. Full Code Listing</a><a class="headerlink" href="#full-code-listing" title="Permalink to this headline">¶</a></h2>
+<p>Here is the complete code listing for our running example, enhanced with
+the LLVM JIT and optimizer. To build this example, use:</p>
+<div class="highlight-bash"><div class="highlight"><pre><span class="c"># Compile</span>
+clang++ -g toy.cpp <span class="sb">`</span>llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native<span class="sb">`</span> -O3 -o toy
+<span class="c"># Run</span>
+./toy
+</pre></div>
+</div>
+<p>If you are compiling this on Linux, make sure to add the “-rdynamic”
+option as well. This makes sure that the external functions are resolved
+properly at runtime.</p>
+<p>Here is the code:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include "llvm/Analysis/Passes.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/ExecutionEngine.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/MCJIT.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/SectionMemoryManager.h"</span>
+<span class="cp">#include "llvm/IR/DataLayout.h"</span>
+<span class="cp">#include "llvm/IR/DerivedTypes.h"</span>
+<span class="cp">#include "llvm/IR/IRBuilder.h"</span>
+<span class="cp">#include "llvm/IR/LLVMContext.h"</span>
+<span class="cp">#include "llvm/IR/LegacyPassManager.h"</span>
+<span class="cp">#include "llvm/IR/Module.h"</span>
+<span class="cp">#include "llvm/IR/Verifier.h"</span>
+<span class="cp">#include "llvm/Support/TargetSelect.h"</span>
+<span class="cp">#include "llvm/Transforms/Scalar.h"</span>
+<span class="cp">#include <cctype></span>
+<span class="cp">#include <cstdio></span>
+<span class="cp">#include <map></span>
+<span class="cp">#include <string></span>
+<span class="cp">#include <vector></span>
+<span class="k">using</span> <span class="k">namespace</span> <span class="n">llvm</span><span class="p">;</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Lexer</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">// The lexer returns tokens [0-255] if it is an unknown character, otherwise one</span>
+<span class="c1">// of these for known things.</span>
+<span class="k">enum</span> <span class="n">Token</span> <span class="p">{</span>
+  <span class="n">tok_eof</span> <span class="o">=</span> <span class="o">-</span><span class="mi">1</span><span class="p">,</span>
+
+  <span class="c1">// commands</span>
+  <span class="n">tok_def</span> <span class="o">=</span> <span class="o">-</span><span class="mi">2</span><span class="p">,</span>
+  <span class="n">tok_extern</span> <span class="o">=</span> <span class="o">-</span><span class="mi">3</span><span class="p">,</span>
+
+  <span class="c1">// primary</span>
+  <span class="n">tok_identifier</span> <span class="o">=</span> <span class="o">-</span><span class="mi">4</span><span class="p">,</span>
+  <span class="n">tok_number</span> <span class="o">=</span> <span class="o">-</span><span class="mi">5</span>
+<span class="p">};</span>
+
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdentifierStr</span><span class="p">;</span> <span class="c1">// Filled in if tok_identifier</span>
+<span class="k">static</span> <span class="kt">double</span> <span class="n">NumVal</span><span class="p">;</span>             <span class="c1">// Filled in if tok_number</span>
+
+<span class="c1">/// gettok - Return the next token from standard input.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">gettok</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">static</span> <span class="kt">int</span> <span class="n">LastChar</span> <span class="o">=</span> <span class="sc">' '</span><span class="p">;</span>
+
+  <span class="c1">// Skip any whitespace.</span>
+  <span class="k">while</span> <span class="p">(</span><span class="n">isspace</span><span class="p">(</span><span class="n">LastChar</span><span class="p">))</span>
+    <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">isalpha</span><span class="p">(</span><span class="n">LastChar</span><span class="p">))</span> <span class="p">{</span> <span class="c1">// identifier: [a-zA-Z][a-zA-Z0-9]*</span>
+    <span class="n">IdentifierStr</span> <span class="o">=</span> <span class="n">LastChar</span><span class="p">;</span>
+    <span class="k">while</span> <span class="p">(</span><span class="n">isalnum</span><span class="p">((</span><span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">())))</span>
+      <span class="n">IdentifierStr</span> <span class="o">+=</span> <span class="n">LastChar</span><span class="p">;</span>
+
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"def"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_def</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"extern"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_extern</span><span class="p">;</span>
+    <span class="k">return</span> <span class="n">tok_identifier</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">isdigit</span><span class="p">(</span><span class="n">LastChar</span><span class="p">)</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">)</span> <span class="p">{</span> <span class="c1">// Number: [0-9.]+</span>
+    <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">NumStr</span><span class="p">;</span>
+    <span class="k">do</span> <span class="p">{</span>
+      <span class="n">NumStr</span> <span class="o">+=</span> <span class="n">LastChar</span><span class="p">;</span>
+      <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+    <span class="p">}</span> <span class="k">while</span> <span class="p">(</span><span class="n">isdigit</span><span class="p">(</span><span class="n">LastChar</span><span class="p">)</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">);</span>
+
+    <span class="n">NumVal</span> <span class="o">=</span> <span class="n">strtod</span><span class="p">(</span><span class="n">NumStr</span><span class="p">.</span><span class="n">c_str</span><span class="p">(),</span> <span class="mi">0</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">tok_number</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'#'</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Comment until end of line.</span>
+    <span class="k">do</span>
+      <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+    <span class="k">while</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">!=</span> <span class="n">EOF</span> <span class="o">&&</span> <span class="n">LastChar</span> <span class="o">!=</span> <span class="sc">'\n'</span> <span class="o">&&</span> <span class="n">LastChar</span> <span class="o">!=</span> <span class="sc">'\r'</span><span class="p">);</span>
+
+    <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">!=</span> <span class="n">EOF</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">gettok</span><span class="p">();</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Check for end of file.  Don't eat the EOF.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="n">EOF</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">tok_eof</span><span class="p">;</span>
+
+  <span class="c1">// Otherwise, just return the character as its ascii value.</span>
+  <span class="kt">int</span> <span class="n">ThisChar</span> <span class="o">=</span> <span class="n">LastChar</span><span class="p">;</span>
+  <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+  <span class="k">return</span> <span class="n">ThisChar</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Abstract Syntax Tree (aka Parse Tree)</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="k">namespace</span> <span class="p">{</span>
+<span class="c1">/// ExprAST - Base class for all expression nodes.</span>
+<span class="k">class</span> <span class="nc">ExprAST</span> <span class="p">{</span>
+<span class="nl">public:</span>
+  <span class="k">virtual</span> <span class="o">~</span><span class="n">ExprAST</span><span class="p">()</span> <span class="p">{}</span>
+  <span class="k">virtual</span> <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// NumberExprAST - Expression class for numeric literals like "1.0".</span>
+<span class="k">class</span> <span class="nc">NumberExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">double</span> <span class="n">Val</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">NumberExprAST</span><span class="p">(</span><span class="kt">double</span> <span class="n">val</span><span class="p">)</span> <span class="o">:</span> <span class="n">Val</span><span class="p">(</span><span class="n">val</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// VariableExprAST - Expression class for referencing a variable, like "a".</span>
+<span class="k">class</span> <span class="nc">VariableExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">VariableExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">name</span><span class="p">)</span> <span class="o">:</span> <span class="n">Name</span><span class="p">(</span><span class="n">name</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// BinaryExprAST - Expression class for a binary operator.</span>
+<span class="k">class</span> <span class="nc">BinaryExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">char</span> <span class="n">Op</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span><span class="p">,</span> <span class="o">*</span><span class="n">RHS</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">BinaryExprAST</span><span class="p">(</span><span class="kt">char</span> <span class="n">op</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">lhs</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">rhs</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Op</span><span class="p">(</span><span class="n">op</span><span class="p">),</span> <span class="n">LHS</span><span class="p">(</span><span class="n">lhs</span><span class="p">),</span> <span class="n">RHS</span><span class="p">(</span><span class="n">rhs</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// CallExprAST - Expression class for function calls.</span>
+<span class="k">class</span> <span class="nc">CallExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Callee</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="n">Args</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">CallExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">callee</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="o">&</span><span class="n">args</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Callee</span><span class="p">(</span><span class="n">callee</span><span class="p">),</span> <span class="n">Args</span><span class="p">(</span><span class="n">args</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// PrototypeAST - This class represents the "prototype" for a function,</span>
+<span class="c1">/// which captures its name, and its argument names (thus implicitly the number</span>
+<span class="c1">/// of arguments the function takes).</span>
+<span class="k">class</span> <span class="nc">PrototypeAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">Args</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">PrototypeAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">name</span><span class="p">,</span> <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="o">&</span><span class="n">args</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Name</span><span class="p">(</span><span class="n">name</span><span class="p">),</span> <span class="n">Args</span><span class="p">(</span><span class="n">args</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+
+<span class="c1">/// FunctionAST - This class represents a function definition itself.</span>
+<span class="k">class</span> <span class="nc">FunctionAST</span> <span class="p">{</span>
+  <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">FunctionAST</span><span class="p">(</span><span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">proto</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span> <span class="o">:</span> <span class="n">Proto</span><span class="p">(</span><span class="n">proto</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+<span class="p">}</span> <span class="c1">// end anonymous namespace</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Parser</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">/// CurTok/getNextToken - Provide a simple token buffer.  CurTok is the current</span>
+<span class="c1">/// token the parser is looking at.  getNextToken reads another token from the</span>
+<span class="c1">/// lexer and updates CurTok with its results.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="n">CurTok</span><span class="p">;</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">getNextToken</span><span class="p">()</span> <span class="p">{</span> <span class="k">return</span> <span class="n">CurTok</span> <span class="o">=</span> <span class="n">gettok</span><span class="p">();</span> <span class="p">}</span>
+
+<span class="c1">/// BinopPrecedence - This holds the precedence for each binary operator that is</span>
+<span class="c1">/// defined.</span>
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="kt">char</span><span class="p">,</span> <span class="kt">int</span><span class="o">></span> <span class="n">BinopPrecedence</span><span class="p">;</span>
+
+<span class="c1">/// GetTokPrecedence - Get the precedence of the pending binary operator token.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">GetTokPrecedence</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+    <span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
+
+  <span class="c1">// Make sure it's a declared binop.</span>
+  <span class="kt">int</span> <span class="n">TokPrec</span> <span class="o">=</span> <span class="n">BinopPrecedence</span><span class="p">[</span><span class="n">CurTok</span><span class="p">];</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><=</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
+  <span class="k">return</span> <span class="n">TokPrec</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// Error* - These are little helper functions for error handling.</span>
+<span class="n">ExprAST</span> <span class="o">*</span><span class="nf">Error</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Error: %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+<span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ErrorP</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+<span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ErrorF</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseExpression</span><span class="p">();</span>
+
+<span class="c1">/// identifierexpr</span>
+<span class="c1">///   ::= identifier</span>
+<span class="c1">///   ::= identifier '(' expression* ')'</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseIdentifierExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat identifier.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'('</span><span class="p">)</span> <span class="c1">// Simple variable ref.</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">VariableExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">);</span>
+
+  <span class="c1">// Call.</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat (</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="n">Args</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Arg</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+      <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Arg</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+      <span class="n">Args</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">Arg</span><span class="p">);</span>
+
+      <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">')'</span><span class="p">)</span>
+        <span class="k">break</span><span class="p">;</span>
+
+      <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span>
+        <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"Expected ')' or ',' in argument list"</span><span class="p">);</span>
+      <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Eat the ')'.</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">CallExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">,</span> <span class="n">Args</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// numberexpr ::= number</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseNumberExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Result</span> <span class="o">=</span> <span class="k">new</span> <span class="n">NumberExprAST</span><span class="p">(</span><span class="n">NumVal</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// consume the number</span>
+  <span class="k">return</span> <span class="n">Result</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// parenexpr ::= '(' expression ')'</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseParenExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat (.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">V</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">V</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected ')'"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat ).</span>
+  <span class="k">return</span> <span class="n">V</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// primary</span>
+<span class="c1">///   ::= identifierexpr</span>
+<span class="c1">///   ::= numberexpr</span>
+<span class="c1">///   ::= parenexpr</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParsePrimary</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="nl">default:</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"unknown token when expecting an expression"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>:
+    <span class="k">return</span> <span class="n">ParseIdentifierExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_number</span>:
+    <span class="k">return</span> <span class="n">ParseNumberExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="sc">'('</span>:
+    <span class="k">return</span> <span class="n">ParseParenExpr</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// binoprhs</span>
+<span class="c1">///   ::= ('+' primary)*</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseBinOpRHS</span><span class="p">(</span><span class="kt">int</span> <span class="n">ExprPrec</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span><span class="p">)</span> <span class="p">{</span>
+  <span class="c1">// If this is a binop, find its precedence.</span>
+  <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+    <span class="kt">int</span> <span class="n">TokPrec</span> <span class="o">=</span> <span class="n">GetTokPrecedence</span><span class="p">();</span>
+
+    <span class="c1">// If this is a binop that binds at least as tightly as the current binop,</span>
+    <span class="c1">// consume it, otherwise we are done.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><</span> <span class="n">ExprPrec</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">LHS</span><span class="p">;</span>
+
+    <span class="c1">// Okay, we know this is a binop.</span>
+    <span class="kt">int</span> <span class="n">BinOp</span> <span class="o">=</span> <span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat binop</span>
+
+    <span class="c1">// Parse the primary expression after the binary operator.</span>
+    <span class="n">ExprAST</span> <span class="o">*</span><span class="n">RHS</span> <span class="o">=</span> <span class="n">ParsePrimary</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">RHS</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+    <span class="c1">// If BinOp binds less tightly with RHS than the operator after RHS, let</span>
+    <span class="c1">// the pending operator take RHS as its LHS.</span>
+    <span class="kt">int</span> <span class="n">NextPrec</span> <span class="o">=</span> <span class="n">GetTokPrecedence</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><</span> <span class="n">NextPrec</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">RHS</span> <span class="o">=</span> <span class="n">ParseBinOpRHS</span><span class="p">(</span><span class="n">TokPrec</span> <span class="o">+</span> <span class="mi">1</span><span class="p">,</span> <span class="n">RHS</span><span class="p">);</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">RHS</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+
+    <span class="c1">// Merge LHS/RHS.</span>
+    <span class="n">LHS</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BinaryExprAST</span><span class="p">(</span><span class="n">BinOp</span><span class="p">,</span> <span class="n">LHS</span><span class="p">,</span> <span class="n">RHS</span><span class="p">);</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// expression</span>
+<span class="c1">///   ::= primary binoprhs</span>
+<span class="c1">///</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseExpression</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span> <span class="o">=</span> <span class="n">ParsePrimary</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">LHS</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="n">ParseBinOpRHS</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">LHS</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// prototype</span>
+<span class="c1">///   ::= id '(' id* ')'</span>
+<span class="k">static</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ParsePrototype</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected function name in prototype"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">FnName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'('</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected '(' in prototype"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">ArgNames</span><span class="p">;</span>
+  <span class="k">while</span> <span class="p">(</span><span class="n">getNextToken</span><span class="p">()</span> <span class="o">==</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="n">ArgNames</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">IdentifierStr</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected ')' in prototype"</span><span class="p">);</span>
+
+  <span class="c1">// success.</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat ')'.</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">PrototypeAST</span><span class="p">(</span><span class="n">FnName</span><span class="p">,</span> <span class="n">ArgNames</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// definition ::= 'def' prototype expression</span>
+<span class="k">static</span> <span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ParseDefinition</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat def.</span>
+  <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span> <span class="o">=</span> <span class="n">ParsePrototype</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Proto</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">E</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">())</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">FunctionAST</span><span class="p">(</span><span class="n">Proto</span><span class="p">,</span> <span class="n">E</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// toplevelexpr ::= expression</span>
+<span class="k">static</span> <span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ParseTopLevelExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">E</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">())</span> <span class="p">{</span>
+    <span class="c1">// Make an anonymous proto.</span>
+    <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span> <span class="o">=</span> <span class="k">new</span> <span class="n">PrototypeAST</span><span class="p">(</span><span class="s">""</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="p">());</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">FunctionAST</span><span class="p">(</span><span class="n">Proto</span><span class="p">,</span> <span class="n">E</span><span class="p">);</span>
+  <span class="p">}</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// external ::= 'extern' prototype</span>
+<span class="k">static</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ParseExtern</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat extern.</span>
+  <span class="k">return</span> <span class="n">ParsePrototype</span><span class="p">();</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Quick and dirty hack</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">// FIXME: Obviously we can do better than this</span>
+<span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">GenerateUniqueName</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">root</span><span class="p">)</span> <span class="p">{</span>
+  <span class="k">static</span> <span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="kt">char</span> <span class="n">s</span><span class="p">[</span><span class="mi">16</span><span class="p">];</span>
+  <span class="n">sprintf</span><span class="p">(</span><span class="n">s</span><span class="p">,</span> <span class="s">"%s%d"</span><span class="p">,</span> <span class="n">root</span><span class="p">,</span> <span class="n">i</span><span class="o">++</span><span class="p">);</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">S</span> <span class="o">=</span> <span class="n">s</span><span class="p">;</span>
+  <span class="k">return</span> <span class="n">S</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">MakeLegalFunctionName</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">NewName</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Name</span><span class="p">.</span><span class="n">length</span><span class="p">())</span>
+    <span class="k">return</span> <span class="n">GenerateUniqueName</span><span class="p">(</span><span class="s">"anon_func_"</span><span class="p">);</span>
+
+  <span class="c1">// Start with what we have</span>
+  <span class="n">NewName</span> <span class="o">=</span> <span class="n">Name</span><span class="p">;</span>
+
+  <span class="c1">// Look for a numberic first character</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">NewName</span><span class="p">.</span><span class="n">find_first_of</span><span class="p">(</span><span class="s">"0123456789"</span><span class="p">)</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">NewName</span><span class="p">.</span><span class="n">insert</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="sc">'n'</span><span class="p">);</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Replace illegal characters with their ASCII equivalent</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">legal_elements</span> <span class="o">=</span>
+      <span class="s">"_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"</span><span class="p">;</span>
+  <span class="kt">size_t</span> <span class="n">pos</span><span class="p">;</span>
+  <span class="k">while</span> <span class="p">((</span><span class="n">pos</span> <span class="o">=</span> <span class="n">NewName</span><span class="p">.</span><span class="n">find_first_not_of</span><span class="p">(</span><span class="n">legal_elements</span><span class="p">))</span> <span class="o">!=</span>
+         <span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">::</span><span class="n">npos</span><span class="p">)</span> <span class="p">{</span>
+    <span class="kt">char</span> <span class="n">old_c</span> <span class="o">=</span> <span class="n">NewName</span><span class="p">.</span><span class="n">at</span><span class="p">(</span><span class="n">pos</span><span class="p">);</span>
+    <span class="kt">char</span> <span class="n">new_str</span><span class="p">[</span><span class="mi">16</span><span class="p">];</span>
+    <span class="n">sprintf</span><span class="p">(</span><span class="n">new_str</span><span class="p">,</span> <span class="s">"%d"</span><span class="p">,</span> <span class="p">(</span><span class="kt">int</span><span class="p">)</span><span class="n">old_c</span><span class="p">);</span>
+    <span class="n">NewName</span> <span class="o">=</span> <span class="n">NewName</span><span class="p">.</span><span class="n">replace</span><span class="p">(</span><span class="n">pos</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="n">new_str</span><span class="p">);</span>
+  <span class="p">}</span>
+
+  <span class="k">return</span> <span class="n">NewName</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// MCJIT helper class</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="k">class</span> <span class="nc">MCJITHelper</span> <span class="p">{</span>
+<span class="nl">public:</span>
+  <span class="n">MCJITHelper</span><span class="p">(</span><span class="n">LLVMContext</span> <span class="o">&</span><span class="n">C</span><span class="p">)</span> <span class="o">:</span> <span class="n">Context</span><span class="p">(</span><span class="n">C</span><span class="p">),</span> <span class="n">OpenModule</span><span class="p">(</span><span class="nb">NULL</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="o">~</span><span class="n">MCJITHelper</span><span class="p">();</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="nf">getFunction</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">FnName</span><span class="p">);</span>
+  <span class="n">Module</span> <span class="o">*</span><span class="nf">getModuleForNewFunction</span><span class="p">();</span>
+  <span class="kt">void</span> <span class="o">*</span><span class="nf">getPointerToFunction</span><span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">F</span><span class="p">);</span>
+  <span class="kt">void</span> <span class="o">*</span><span class="nf">getSymbolAddress</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">Name</span><span class="p">);</span>
+  <span class="kt">void</span> <span class="nf">dump</span><span class="p">();</span>
+
+<span class="nl">private:</span>
+  <span class="k">typedef</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">Module</span> <span class="o">*></span> <span class="n">ModuleVector</span><span class="p">;</span>
+  <span class="k">typedef</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExecutionEngine</span> <span class="o">*></span> <span class="n">EngineVector</span><span class="p">;</span>
+
+  <span class="n">LLVMContext</span> <span class="o">&</span><span class="n">Context</span><span class="p">;</span>
+  <span class="n">Module</span> <span class="o">*</span><span class="n">OpenModule</span><span class="p">;</span>
+  <span class="n">ModuleVector</span> <span class="n">Modules</span><span class="p">;</span>
+  <span class="n">EngineVector</span> <span class="n">Engines</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="k">class</span> <span class="nc">HelpingMemoryManager</span> <span class="o">:</span> <span class="k">public</span> <span class="n">SectionMemoryManager</span> <span class="p">{</span>
+  <span class="n">HelpingMemoryManager</span><span class="p">(</span><span class="k">const</span> <span class="n">HelpingMemoryManager</span> <span class="o">&</span><span class="p">)</span> <span class="o">=</span> <span class="k">delete</span><span class="p">;</span>
+  <span class="kt">void</span> <span class="k">operator</span><span class="o">=</span><span class="p">(</span><span class="k">const</span> <span class="n">HelpingMemoryManager</span> <span class="o">&</span><span class="p">)</span> <span class="o">=</span> <span class="k">delete</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">HelpingMemoryManager</span><span class="p">(</span><span class="n">MCJITHelper</span> <span class="o">*</span><span class="n">Helper</span><span class="p">)</span> <span class="o">:</span> <span class="n">MasterHelper</span><span class="p">(</span><span class="n">Helper</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="o">~</span><span class="n">HelpingMemoryManager</span><span class="p">()</span> <span class="n">override</span> <span class="p">{}</span>
+
+  <span class="c1">/// This method returns the address of the specified symbol.</span>
+  <span class="c1">/// Our implementation will attempt to find symbols in other</span>
+  <span class="c1">/// modules associated with the MCJITHelper to cross link symbols</span>
+  <span class="c1">/// from one generated module to another.</span>
+  <span class="kt">uint64_t</span> <span class="n">getSymbolAddress</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">Name</span><span class="p">)</span> <span class="n">override</span><span class="p">;</span>
+
+<span class="nl">private:</span>
+  <span class="n">MCJITHelper</span> <span class="o">*</span><span class="n">MasterHelper</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="kt">uint64_t</span> <span class="n">HelpingMemoryManager</span><span class="o">::</span><span class="n">getSymbolAddress</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">Name</span><span class="p">)</span> <span class="p">{</span>
+  <span class="kt">uint64_t</span> <span class="n">FnAddr</span> <span class="o">=</span> <span class="n">SectionMemoryManager</span><span class="o">::</span><span class="n">getSymbolAddress</span><span class="p">(</span><span class="n">Name</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">FnAddr</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">FnAddr</span><span class="p">;</span>
+
+  <span class="kt">uint64_t</span> <span class="n">HelperFun</span> <span class="o">=</span> <span class="p">(</span><span class="kt">uint64_t</span><span class="p">)</span><span class="n">MasterHelper</span><span class="o">-></span><span class="n">getSymbolAddress</span><span class="p">(</span><span class="n">Name</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">HelperFun</span><span class="p">)</span>
+    <span class="n">report_fatal_error</span><span class="p">(</span><span class="s">"Program used extern function '"</span> <span class="o">+</span> <span class="n">Name</span> <span class="o">+</span>
+                       <span class="s">"' which could not be resolved!"</span><span class="p">);</span>
+
+  <span class="k">return</span> <span class="n">HelperFun</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">MCJITHelper</span><span class="o">::~</span><span class="n">MCJITHelper</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">OpenModule</span><span class="p">)</span>
+    <span class="k">delete</span> <span class="n">OpenModule</span><span class="p">;</span>
+  <span class="n">EngineVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">begin</span> <span class="o">=</span> <span class="n">Engines</span><span class="p">.</span><span class="n">begin</span><span class="p">();</span>
+  <span class="n">EngineVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">end</span> <span class="o">=</span> <span class="n">Engines</span><span class="p">.</span><span class="n">end</span><span class="p">();</span>
+  <span class="n">EngineVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">it</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="n">it</span> <span class="o">=</span> <span class="n">begin</span><span class="p">;</span> <span class="n">it</span> <span class="o">!=</span> <span class="n">end</span><span class="p">;</span> <span class="o">++</span><span class="n">it</span><span class="p">)</span>
+    <span class="k">delete</span> <span class="o">*</span><span class="n">it</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Function</span> <span class="o">*</span><span class="n">MCJITHelper</span><span class="o">::</span><span class="n">getFunction</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">FnName</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">ModuleVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">begin</span> <span class="o">=</span> <span class="n">Modules</span><span class="p">.</span><span class="n">begin</span><span class="p">();</span>
+  <span class="n">ModuleVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">end</span> <span class="o">=</span> <span class="n">Modules</span><span class="p">.</span><span class="n">end</span><span class="p">();</span>
+  <span class="n">ModuleVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">it</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="n">it</span> <span class="o">=</span> <span class="n">begin</span><span class="p">;</span> <span class="n">it</span> <span class="o">!=</span> <span class="n">end</span><span class="p">;</span> <span class="o">++</span><span class="n">it</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="p">(</span><span class="o">*</span><span class="n">it</span><span class="p">)</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">FnName</span><span class="p">);</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">F</span><span class="p">)</span> <span class="p">{</span>
+      <span class="k">if</span> <span class="p">(</span><span class="o">*</span><span class="n">it</span> <span class="o">==</span> <span class="n">OpenModule</span><span class="p">)</span>
+        <span class="k">return</span> <span class="n">F</span><span class="p">;</span>
+
+      <span class="n">assert</span><span class="p">(</span><span class="n">OpenModule</span> <span class="o">!=</span> <span class="nb">NULL</span><span class="p">);</span>
+
+      <span class="c1">// This function is in a module that has already been JITed.</span>
+      <span class="c1">// We need to generate a new prototype for external linkage.</span>
+      <span class="n">Function</span> <span class="o">*</span><span class="n">PF</span> <span class="o">=</span> <span class="n">OpenModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">FnName</span><span class="p">);</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">PF</span> <span class="o">&&</span> <span class="o">!</span><span class="n">PF</span><span class="o">-></span><span class="n">empty</span><span class="p">())</span> <span class="p">{</span>
+        <span class="n">ErrorF</span><span class="p">(</span><span class="s">"redefinition of function across modules"</span><span class="p">);</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+      <span class="p">}</span>
+
+      <span class="c1">// If we don't have a prototype yet, create one.</span>
+      <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">PF</span><span class="p">)</span>
+        <span class="n">PF</span> <span class="o">=</span> <span class="n">Function</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">F</span><span class="o">-></span><span class="n">getFunctionType</span><span class="p">(),</span> <span class="n">Function</span><span class="o">::</span><span class="n">ExternalLinkage</span><span class="p">,</span>
+                              <span class="n">FnName</span><span class="p">,</span> <span class="n">OpenModule</span><span class="p">);</span>
+      <span class="k">return</span> <span class="n">PF</span><span class="p">;</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+  <span class="k">return</span> <span class="nb">NULL</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Module</span> <span class="o">*</span><span class="n">MCJITHelper</span><span class="o">::</span><span class="n">getModuleForNewFunction</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// If we have a Module that hasn't been JITed, use that.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">OpenModule</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">OpenModule</span><span class="p">;</span>
+
+  <span class="c1">// Otherwise create a new Module.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">ModName</span> <span class="o">=</span> <span class="n">GenerateUniqueName</span><span class="p">(</span><span class="s">"mcjit_module_"</span><span class="p">);</span>
+  <span class="n">Module</span> <span class="o">*</span><span class="n">M</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Module</span><span class="p">(</span><span class="n">ModName</span><span class="p">,</span> <span class="n">Context</span><span class="p">);</span>
+  <span class="n">Modules</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">M</span><span class="p">);</span>
+  <span class="n">OpenModule</span> <span class="o">=</span> <span class="n">M</span><span class="p">;</span>
+  <span class="k">return</span> <span class="n">M</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="o">*</span><span class="n">MCJITHelper</span><span class="o">::</span><span class="n">getPointerToFunction</span><span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">F</span><span class="p">)</span> <span class="p">{</span>
+  <span class="c1">// See if an existing instance of MCJIT has this function.</span>
+  <span class="n">EngineVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">begin</span> <span class="o">=</span> <span class="n">Engines</span><span class="p">.</span><span class="n">begin</span><span class="p">();</span>
+  <span class="n">EngineVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">end</span> <span class="o">=</span> <span class="n">Engines</span><span class="p">.</span><span class="n">end</span><span class="p">();</span>
+  <span class="n">EngineVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">it</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="n">it</span> <span class="o">=</span> <span class="n">begin</span><span class="p">;</span> <span class="n">it</span> <span class="o">!=</span> <span class="n">end</span><span class="p">;</span> <span class="o">++</span><span class="n">it</span><span class="p">)</span> <span class="p">{</span>
+    <span class="kt">void</span> <span class="o">*</span><span class="n">P</span> <span class="o">=</span> <span class="p">(</span><span class="o">*</span><span class="n">it</span><span class="p">)</span><span class="o">-></span><span class="n">getPointerToFunction</span><span class="p">(</span><span class="n">F</span><span class="p">);</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">P</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">P</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="c1">// If we didn't find the function, see if we can generate it.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">OpenModule</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">ErrStr</span><span class="p">;</span>
+    <span class="n">ExecutionEngine</span> <span class="o">*</span><span class="n">NewEngine</span> <span class="o">=</span>
+        <span class="n">EngineBuilder</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">unique_ptr</span><span class="o"><</span><span class="n">Module</span><span class="o">></span><span class="p">(</span><span class="n">OpenModule</span><span class="p">))</span>
+            <span class="p">.</span><span class="n">setErrorStr</span><span class="p">(</span><span class="o">&</span><span class="n">ErrStr</span><span class="p">)</span>
+            <span class="p">.</span><span class="n">setMCJITMemoryManager</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">unique_ptr</span><span class="o"><</span><span class="n">HelpingMemoryManager</span><span class="o">></span><span class="p">(</span>
+                <span class="k">new</span> <span class="n">HelpingMemoryManager</span><span class="p">(</span><span class="k">this</span><span class="p">)))</span>
+            <span class="p">.</span><span class="n">create</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">NewEngine</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Could not create ExecutionEngine: %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">ErrStr</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+      <span class="n">exit</span><span class="p">(</span><span class="mi">1</span><span class="p">);</span>
+    <span class="p">}</span>
+
+    <span class="c1">// Create a function pass manager for this engine</span>
+    <span class="k">auto</span> <span class="o">*</span><span class="n">FPM</span> <span class="o">=</span> <span class="k">new</span> <span class="n">legacy</span><span class="o">::</span><span class="n">FunctionPassManager</span><span class="p">(</span><span class="n">OpenModule</span><span class="p">);</span>
+
+    <span class="c1">// Set up the optimizer pipeline.  Start with registering info about how the</span>
+    <span class="c1">// target lays out data structures.</span>
+    <span class="n">OpenModule</span><span class="o">-></span><span class="n">setDataLayout</span><span class="p">(</span><span class="o">*</span><span class="n">NewEngine</span><span class="o">-></span><span class="n">getDataLayout</span><span class="p">());</span>
+    <span class="c1">// Provide basic AliasAnalysis support for GVN.</span>
+    <span class="n">FPM</span><span class="o">-></span><span class="n">add</span><span class="p">(</span><span class="n">createBasicAliasAnalysisPass</span><span class="p">());</span>
+    <span class="c1">// Promote allocas to registers.</span>
+    <span class="n">FPM</span><span class="o">-></span><span class="n">add</span><span class="p">(</span><span class="n">createPromoteMemoryToRegisterPass</span><span class="p">());</span>
+    <span class="c1">// Do simple "peephole" optimizations and bit-twiddling optzns.</span>
+    <span class="n">FPM</span><span class="o">-></span><span class="n">add</span><span class="p">(</span><span class="n">createInstructionCombiningPass</span><span class="p">());</span>
+    <span class="c1">// Reassociate expressions.</span>
+    <span class="n">FPM</span><span class="o">-></span><span class="n">add</span><span class="p">(</span><span class="n">createReassociatePass</span><span class="p">());</span>
+    <span class="c1">// Eliminate Common SubExpressions.</span>
+    <span class="n">FPM</span><span class="o">-></span><span class="n">add</span><span class="p">(</span><span class="n">createGVNPass</span><span class="p">());</span>
+    <span class="c1">// Simplify the control flow graph (deleting unreachable blocks, etc).</span>
+    <span class="n">FPM</span><span class="o">-></span><span class="n">add</span><span class="p">(</span><span class="n">createCFGSimplificationPass</span><span class="p">());</span>
+    <span class="n">FPM</span><span class="o">-></span><span class="n">doInitialization</span><span class="p">();</span>
+
+    <span class="c1">// For each function in the module</span>
+    <span class="n">Module</span><span class="o">::</span><span class="n">iterator</span> <span class="n">it</span><span class="p">;</span>
+    <span class="n">Module</span><span class="o">::</span><span class="n">iterator</span> <span class="n">end</span> <span class="o">=</span> <span class="n">OpenModule</span><span class="o">-></span><span class="n">end</span><span class="p">();</span>
+    <span class="k">for</span> <span class="p">(</span><span class="n">it</span> <span class="o">=</span> <span class="n">OpenModule</span><span class="o">-></span><span class="n">begin</span><span class="p">();</span> <span class="n">it</span> <span class="o">!=</span> <span class="n">end</span><span class="p">;</span> <span class="o">++</span><span class="n">it</span><span class="p">)</span> <span class="p">{</span>
+      <span class="c1">// Run the FPM on this function</span>
+      <span class="n">FPM</span><span class="o">-></span><span class="n">run</span><span class="p">(</span><span class="o">*</span><span class="n">it</span><span class="p">);</span>
+    <span class="p">}</span>
+
+    <span class="c1">// We don't need this anymore</span>
+    <span class="k">delete</span> <span class="n">FPM</span><span class="p">;</span>
+
+    <span class="n">OpenModule</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
+    <span class="n">Engines</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">NewEngine</span><span class="p">);</span>
+    <span class="n">NewEngine</span><span class="o">-></span><span class="n">finalizeObject</span><span class="p">();</span>
+    <span class="k">return</span> <span class="n">NewEngine</span><span class="o">-></span><span class="n">getPointerToFunction</span><span class="p">(</span><span class="n">F</span><span class="p">);</span>
+  <span class="p">}</span>
+  <span class="k">return</span> <span class="nb">NULL</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="o">*</span><span class="n">MCJITHelper</span><span class="o">::</span><span class="n">getSymbolAddress</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">Name</span><span class="p">)</span> <span class="p">{</span>
+  <span class="c1">// Look for the symbol in each of our execution engines.</span>
+  <span class="n">EngineVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">begin</span> <span class="o">=</span> <span class="n">Engines</span><span class="p">.</span><span class="n">begin</span><span class="p">();</span>
+  <span class="n">EngineVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">end</span> <span class="o">=</span> <span class="n">Engines</span><span class="p">.</span><span class="n">end</span><span class="p">();</span>
+  <span class="n">EngineVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">it</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="n">it</span> <span class="o">=</span> <span class="n">begin</span><span class="p">;</span> <span class="n">it</span> <span class="o">!=</span> <span class="n">end</span><span class="p">;</span> <span class="o">++</span><span class="n">it</span><span class="p">)</span> <span class="p">{</span>
+    <span class="kt">uint64_t</span> <span class="n">FAddr</span> <span class="o">=</span> <span class="p">(</span><span class="o">*</span><span class="n">it</span><span class="p">)</span><span class="o">-></span><span class="n">getFunctionAddress</span><span class="p">(</span><span class="n">Name</span><span class="p">);</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">FAddr</span><span class="p">)</span> <span class="p">{</span>
+      <span class="k">return</span> <span class="p">(</span><span class="kt">void</span> <span class="o">*</span><span class="p">)</span><span class="n">FAddr</span><span class="p">;</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+  <span class="k">return</span> <span class="nb">NULL</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="n">MCJITHelper</span><span class="o">::</span><span class="n">dump</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">ModuleVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">begin</span> <span class="o">=</span> <span class="n">Modules</span><span class="p">.</span><span class="n">begin</span><span class="p">();</span>
+  <span class="n">ModuleVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">end</span> <span class="o">=</span> <span class="n">Modules</span><span class="p">.</span><span class="n">end</span><span class="p">();</span>
+  <span class="n">ModuleVector</span><span class="o">::</span><span class="n">iterator</span> <span class="n">it</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="n">it</span> <span class="o">=</span> <span class="n">begin</span><span class="p">;</span> <span class="n">it</span> <span class="o">!=</span> <span class="n">end</span><span class="p">;</span> <span class="o">++</span><span class="n">it</span><span class="p">)</span>
+    <span class="p">(</span><span class="o">*</span><span class="n">it</span><span class="p">)</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+<span class="p">}</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Code Generation</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="k">static</span> <span class="n">MCJITHelper</span> <span class="o">*</span><span class="n">JITHelper</span><span class="p">;</span>
+<span class="k">static</span> <span class="n">IRBuilder</span><span class="o"><></span> <span class="n">Builder</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">());</span>
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">Value</span> <span class="o">*></span> <span class="n">NamedValues</span><span class="p">;</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="nf">ErrorV</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">NumberExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">return</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="n">Val</span><span class="p">));</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">VariableExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Look this variable up in the function.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">V</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">Name</span><span class="p">];</span>
+  <span class="k">return</span> <span class="n">V</span> <span class="o">?</span> <span class="n">V</span> <span class="o">:</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown variable name"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">BinaryExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">L</span> <span class="o">=</span> <span class="n">LHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">R</span> <span class="o">=</span> <span class="n">RHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">L</span> <span class="o">==</span> <span class="mi">0</span> <span class="o">||</span> <span class="n">R</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">switch</span> <span class="p">(</span><span class="n">Op</span><span class="p">)</span> <span class="p">{</span>
+  <span class="k">case</span> <span class="sc">'+'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFAdd</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"addtmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'-'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFSub</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"subtmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'*'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFMul</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"multmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'<'</span>:
+    <span class="n">L</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpULT</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"cmptmp"</span><span class="p">);</span>
+    <span class="c1">// Convert bool 0/1 to double 0.0 or 1.0</span>
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateUIToFP</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span>
+                                <span class="s">"booltmp"</span><span class="p">);</span>
+  <span class="nl">default:</span>
+    <span class="k">return</span> <span class="nf">ErrorV</span><span class="p">(</span><span class="s">"invalid binary operator"</span><span class="p">);</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">CallExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Look up the name in the global module table.</span>
+  <span class="n">Function</span> <span class="o">*</span><span class="n">CalleeF</span> <span class="o">=</span> <span class="n">JITHelper</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">Callee</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CalleeF</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown function referenced"</span><span class="p">);</span>
+
+  <span class="c1">// If argument mismatch error.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CalleeF</span><span class="o">-></span><span class="n">arg_size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">())</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Incorrect # arguments passed"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">Value</span> <span class="o">*></span> <span class="n">ArgsV</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">ArgsV</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">Args</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="o">-></span><span class="n">Codegen</span><span class="p">());</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">ArgsV</span><span class="p">.</span><span class="n">back</span><span class="p">()</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">CalleeF</span><span class="p">,</span> <span class="n">ArgsV</span><span class="p">,</span> <span class="s">"calltmp"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Function</span> <span class="o">*</span><span class="n">PrototypeAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Make the function type:  double(double,double) etc.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">Type</span> <span class="o">*></span> <span class="n">Doubles</span><span class="p">(</span><span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">(),</span>
+                              <span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()));</span>
+  <span class="n">FunctionType</span> <span class="o">*</span><span class="n">FT</span> <span class="o">=</span>
+      <span class="n">FunctionType</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="n">Doubles</span><span class="p">,</span> <span class="nb">false</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">FnName</span> <span class="o">=</span> <span class="n">MakeLegalFunctionName</span><span class="p">(</span><span class="n">Name</span><span class="p">);</span>
+
+  <span class="n">Module</span> <span class="o">*</span><span class="n">M</span> <span class="o">=</span> <span class="n">JITHelper</span><span class="o">-></span><span class="n">getModuleForNewFunction</span><span class="p">();</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">Function</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">FT</span><span class="p">,</span> <span class="n">Function</span><span class="o">::</span><span class="n">ExternalLinkage</span><span class="p">,</span> <span class="n">FnName</span><span class="p">,</span> <span class="n">M</span><span class="p">);</span>
+
+  <span class="c1">// If F conflicted, there was already something named 'Name'.  If it has a</span>
+  <span class="c1">// body, don't allow redefinition or reextern.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">F</span><span class="o">-></span><span class="n">getName</span><span class="p">()</span> <span class="o">!=</span> <span class="n">FnName</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Delete the one we just made and get the existing one.</span>
+    <span class="n">F</span><span class="o">-></span><span class="n">eraseFromParent</span><span class="p">();</span>
+    <span class="n">F</span> <span class="o">=</span> <span class="n">JITHelper</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">Name</span><span class="p">);</span>
+    <span class="c1">// If F already has a body, reject this.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">F</span><span class="o">-></span><span class="n">empty</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">ErrorF</span><span class="p">(</span><span class="s">"redefinition of function"</span><span class="p">);</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+
+    <span class="c1">// If F took a different number of args, reject.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">F</span><span class="o">-></span><span class="n">arg_size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">ErrorF</span><span class="p">(</span><span class="s">"redefinition of function with different # args"</span><span class="p">);</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Set names for all arguments.</span>
+  <span class="kt">unsigned</span> <span class="n">Idx</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="n">Function</span><span class="o">::</span><span class="n">arg_iterator</span> <span class="n">AI</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">arg_begin</span><span class="p">();</span> <span class="n">Idx</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span>
+       <span class="o">++</span><span class="n">AI</span><span class="p">,</span> <span class="o">++</span><span class="n">Idx</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">AI</span><span class="o">-></span><span class="n">setName</span><span class="p">(</span><span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]);</span>
+
+    <span class="c1">// Add arguments to variable symbol table.</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]]</span> <span class="o">=</span> <span class="n">AI</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">return</span> <span class="n">F</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Function</span> <span class="o">*</span><span class="n">FunctionAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">NamedValues</span><span class="p">.</span><span class="n">clear</span><span class="p">();</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Proto</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">TheFunction</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Create a new basic block to start insertion into.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">BB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"entry"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">BB</span><span class="p">);</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">Value</span> <span class="o">*</span><span class="n">RetVal</span> <span class="o">=</span> <span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+    <span class="c1">// Finish off the function.</span>
+    <span class="n">Builder</span><span class="p">.</span><span class="n">CreateRet</span><span class="p">(</span><span class="n">RetVal</span><span class="p">);</span>
+
+    <span class="c1">// Validate the generated code, checking for consistency.</span>
+    <span class="n">verifyFunction</span><span class="p">(</span><span class="o">*</span><span class="n">TheFunction</span><span class="p">);</span>
+
+    <span class="k">return</span> <span class="n">TheFunction</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Error reading body, remove function.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">eraseFromParent</span><span class="p">();</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Top-Level parsing and JIT Driver</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="n">HandleDefinition</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">FunctionAST</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">ParseDefinition</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">LF</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Read function definition:"</span><span class="p">);</span>
+      <span class="n">LF</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="n">HandleExtern</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">P</span> <span class="o">=</span> <span class="n">ParseExtern</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">P</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Read extern: "</span><span class="p">);</span>
+      <span class="n">F</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="n">HandleTopLevelExpression</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Evaluate a top-level expression into an anonymous function.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">FunctionAST</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">ParseTopLevelExpr</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">LF</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="c1">// JIT the function, returning a function pointer.</span>
+      <span class="kt">void</span> <span class="o">*</span><span class="n">FPtr</span> <span class="o">=</span> <span class="n">JITHelper</span><span class="o">-></span><span class="n">getPointerToFunction</span><span class="p">(</span><span class="n">LF</span><span class="p">);</span>
+
+      <span class="c1">// Cast it to the right type (takes no arguments, returns a double) so we</span>
+      <span class="c1">// can call it as a native function.</span>
+      <span class="kt">double</span> <span class="p">(</span><span class="o">*</span><span class="n">FP</span><span class="p">)()</span> <span class="o">=</span> <span class="p">(</span><span class="kt">double</span> <span class="p">(</span><span class="o">*</span><span class="p">)())(</span><span class="kt">intptr_t</span><span class="p">)</span><span class="n">FPtr</span><span class="p">;</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Evaluated to %f</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">FP</span><span class="p">());</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// top ::= definition | external | expression | ';'</span>
+<span class="k">static</span> <span class="kt">void</span> <span class="n">MainLoop</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"ready> "</span><span class="p">);</span>
+    <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">case</span> <span class="n">tok_eof</span>:
+      <span class="k">return</span><span class="p">;</span>
+    <span class="k">case</span> <span class="sc">';'</span>:
+      <span class="n">getNextToken</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span> <span class="c1">// ignore top-level semicolons.</span>
+    <span class="k">case</span> <span class="n">tok_def</span>:
+      <span class="n">HandleDefinition</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="k">case</span> <span class="n">tok_extern</span>:
+      <span class="n">HandleExtern</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="nl">default:</span>
+      <span class="n">HandleTopLevelExpression</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// "Library" functions that can be "extern'd" from user code.</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">/// putchard - putchar that takes a double and returns 0.</span>
+<span class="k">extern</span> <span class="s">"C"</span> <span class="kt">double</span> <span class="n">putchard</span><span class="p">(</span><span class="kt">double</span> <span class="n">X</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">putchar</span><span class="p">((</span><span class="kt">char</span><span class="p">)</span><span class="n">X</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Main driver code.</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="kt">int</span> <span class="n">main</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">InitializeNativeTarget</span><span class="p">();</span>
+  <span class="n">InitializeNativeTargetAsmPrinter</span><span class="p">();</span>
+  <span class="n">InitializeNativeTargetAsmParser</span><span class="p">();</span>
+  <span class="n">LLVMContext</span> <span class="o">&</span><span class="n">Context</span> <span class="o">=</span> <span class="n">getGlobalContext</span><span class="p">();</span>
+  <span class="n">JITHelper</span> <span class="o">=</span> <span class="k">new</span> <span class="n">MCJITHelper</span><span class="p">(</span><span class="n">Context</span><span class="p">);</span>
+
+  <span class="c1">// Install standard binary operators.</span>
+  <span class="c1">// 1 is lowest precedence.</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'<'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'+'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'-'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'*'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">40</span><span class="p">;</span> <span class="c1">// highest.</span>
+
+  <span class="c1">// Prime the first token.</span>
+  <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"ready> "</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="c1">// Run the main "interpreter loop" now.</span>
+  <span class="n">MainLoop</span><span class="p">();</span>
+
+  <span class="c1">// Print out all of the generated code.</span>
+  <span class="n">JITHelper</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p><a class="reference external" href="LangImpl5.html">Next: Extending the language: control flow</a></p>
+</div>
+</div>
+
+
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+  <div class="section" id="kaleidoscope-extending-the-language-control-flow">
+<h1>5. Kaleidoscope: Extending the Language: Control Flow<a class="headerlink" href="#kaleidoscope-extending-the-language-control-flow" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#chapter-5-introduction" id="id1">Chapter 5 Introduction</a></li>
+<li><a class="reference internal" href="#if-then-else" id="id2">If/Then/Else</a><ul>
+<li><a class="reference internal" href="#lexer-extensions-for-if-then-else" id="id3">Lexer Extensions for If/Then/Else</a></li>
+<li><a class="reference internal" href="#ast-extensions-for-if-then-else" id="id4">AST Extensions for If/Then/Else</a></li>
+<li><a class="reference internal" href="#parser-extensions-for-if-then-else" id="id5">Parser Extensions for If/Then/Else</a></li>
+<li><a class="reference internal" href="#llvm-ir-for-if-then-else" id="id6">LLVM IR for If/Then/Else</a></li>
+<li><a class="reference internal" href="#code-generation-for-if-then-else" id="id7">Code Generation for If/Then/Else</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#for-loop-expression" id="id8">‘for’ Loop Expression</a><ul>
+<li><a class="reference internal" href="#lexer-extensions-for-the-for-loop" id="id9">Lexer Extensions for the ‘for’ Loop</a></li>
+<li><a class="reference internal" href="#ast-extensions-for-the-for-loop" id="id10">AST Extensions for the ‘for’ Loop</a></li>
+<li><a class="reference internal" href="#parser-extensions-for-the-for-loop" id="id11">Parser Extensions for the ‘for’ Loop</a></li>
+<li><a class="reference internal" href="#llvm-ir-for-the-for-loop" id="id12">LLVM IR for the ‘for’ Loop</a></li>
+<li><a class="reference internal" href="#code-generation-for-the-for-loop" id="id13">Code Generation for the ‘for’ Loop</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#full-code-listing" id="id14">Full Code Listing</a></li>
+</ul>
+</div>
+<div class="section" id="chapter-5-introduction">
+<h2><a class="toc-backref" href="#id1">5.1. Chapter 5 Introduction</a><a class="headerlink" href="#chapter-5-introduction" title="Permalink to this headline">¶</a></h2>
+<p>Welcome to Chapter 5 of the “<a class="reference external" href="index.html">Implementing a language with
+LLVM</a>” tutorial. Parts 1-4 described the implementation of
+the simple Kaleidoscope language and included support for generating
+LLVM IR, followed by optimizations and a JIT compiler. Unfortunately, as
+presented, Kaleidoscope is mostly useless: it has no control flow other
+than call and return. This means that you can’t have conditional
+branches in the code, significantly limiting its power. In this episode
+of “build that compiler”, we’ll extend Kaleidoscope to have an
+if/then/else expression plus a simple ‘for’ loop.</p>
+</div>
+<div class="section" id="if-then-else">
+<h2><a class="toc-backref" href="#id2">5.2. If/Then/Else</a><a class="headerlink" href="#if-then-else" title="Permalink to this headline">¶</a></h2>
+<p>Extending Kaleidoscope to support if/then/else is quite straightforward.
+It basically requires adding support for this “new” concept to the
+lexer, parser, AST, and LLVM code emitter. This example is nice, because
+it shows how easy it is to “grow” a language over time, incrementally
+extending it as new ideas are discovered.</p>
+<p>Before we get going on “how” we add this extension, lets talk about
+“what” we want. The basic idea is that we want to be able to write this
+sort of thing:</p>
+<div class="highlight-python"><div class="highlight"><pre>def fib(x)
+  if x < 3 then
+    1
+  else
+    fib(x-1)+fib(x-2);
+</pre></div>
+</div>
+<p>In Kaleidoscope, every construct is an expression: there are no
+statements. As such, the if/then/else expression needs to return a value
+like any other. Since we’re using a mostly functional form, we’ll have
+it evaluate its conditional, then return the ‘then’ or ‘else’ value
+based on how the condition was resolved. This is very similar to the C
+”?:” expression.</p>
+<p>The semantics of the if/then/else expression is that it evaluates the
+condition to a boolean equality value: 0.0 is considered to be false and
+everything else is considered to be true. If the condition is true, the
+first subexpression is evaluated and returned, if the condition is
+false, the second subexpression is evaluated and returned. Since
+Kaleidoscope allows side-effects, this behavior is important to nail
+down.</p>
+<p>Now that we know what we “want”, lets break this down into its
+constituent pieces.</p>
+<div class="section" id="lexer-extensions-for-if-then-else">
+<h3><a class="toc-backref" href="#id3">5.2.1. Lexer Extensions for If/Then/Else</a><a class="headerlink" href="#lexer-extensions-for-if-then-else" title="Permalink to this headline">¶</a></h3>
+<p>The lexer extensions are straightforward. First we add new enum values
+for the relevant tokens:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// control</span>
+<span class="n">tok_if</span> <span class="o">=</span> <span class="o">-</span><span class="mi">6</span><span class="p">,</span> <span class="n">tok_then</span> <span class="o">=</span> <span class="o">-</span><span class="mi">7</span><span class="p">,</span> <span class="n">tok_else</span> <span class="o">=</span> <span class="o">-</span><span class="mi">8</span><span class="p">,</span>
+</pre></div>
+</div>
+<p>Once we have that, we recognize the new keywords in the lexer. This is
+pretty simple stuff:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="p">...</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"def"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_def</span><span class="p">;</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"extern"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_extern</span><span class="p">;</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"if"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_if</span><span class="p">;</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"then"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_then</span><span class="p">;</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"else"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_else</span><span class="p">;</span>
+<span class="k">return</span> <span class="n">tok_identifier</span><span class="p">;</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="ast-extensions-for-if-then-else">
+<h3><a class="toc-backref" href="#id4">5.2.2. AST Extensions for If/Then/Else</a><a class="headerlink" href="#ast-extensions-for-if-then-else" title="Permalink to this headline">¶</a></h3>
+<p>To represent the new expression we add a new AST node for it:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// IfExprAST - Expression class for if/then/else.</span>
+<span class="k">class</span> <span class="nc">IfExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Cond</span><span class="p">,</span> <span class="o">*</span><span class="n">Then</span><span class="p">,</span> <span class="o">*</span><span class="n">Else</span><span class="p">;</span>
+<span class="nl">public:</span>
+  <span class="n">IfExprAST</span><span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">cond</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">then</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">_else</span><span class="p">)</span>
+    <span class="o">:</span> <span class="n">Cond</span><span class="p">(</span><span class="n">cond</span><span class="p">),</span> <span class="n">Then</span><span class="p">(</span><span class="n">then</span><span class="p">),</span> <span class="n">Else</span><span class="p">(</span><span class="n">_else</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="k">virtual</span> <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>The AST node just has pointers to the various subexpressions.</p>
+</div>
+<div class="section" id="parser-extensions-for-if-then-else">
+<h3><a class="toc-backref" href="#id5">5.2.3. Parser Extensions for If/Then/Else</a><a class="headerlink" href="#parser-extensions-for-if-then-else" title="Permalink to this headline">¶</a></h3>
+<p>Now that we have the relevant tokens coming from the lexer and we have
+the AST node to build, our parsing logic is relatively straightforward.
+First we define a new parsing function:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// ifexpr ::= 'if' expression 'then' expression 'else' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseIfExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span>  <span class="c1">// eat the if.</span>
+
+  <span class="c1">// condition.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Cond</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Cond</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_then</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected then"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>  <span class="c1">// eat the then</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Then</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Then</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_else</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected else"</span><span class="p">);</span>
+
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Else</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Else</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">IfExprAST</span><span class="p">(</span><span class="n">Cond</span><span class="p">,</span> <span class="n">Then</span><span class="p">,</span> <span class="n">Else</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Next we hook it up as a primary expression:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParsePrimary</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="nl">default:</span> <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"unknown token when expecting an expression"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>: <span class="k">return</span> <span class="n">ParseIdentifierExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_number</span>:     <span class="k">return</span> <span class="n">ParseNumberExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="sc">'('</span>:            <span class="k">return</span> <span class="n">ParseParenExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_if</span>:         <span class="k">return</span> <span class="n">ParseIfExpr</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="llvm-ir-for-if-then-else">
+<h3><a class="toc-backref" href="#id6">5.2.4. LLVM IR for If/Then/Else</a><a class="headerlink" href="#llvm-ir-for-if-then-else" title="Permalink to this headline">¶</a></h3>
+<p>Now that we have it parsing and building the AST, the final piece is
+adding LLVM code generation support. This is the most interesting part
+of the if/then/else example, because this is where it starts to
+introduce new concepts. All of the code above has been thoroughly
+described in previous chapters.</p>
+<p>To motivate the code we want to produce, lets take a look at a simple
+example. Consider:</p>
+<div class="highlight-python"><div class="highlight"><pre>extern foo();
+extern bar();
+def baz(x) if x then foo() else bar();
+</pre></div>
+</div>
+<p>If you disable optimizations, the code you’ll (soon) get from
+Kaleidoscope looks like this:</p>
+<div class="highlight-llvm"><div class="highlight"><pre><span class="k">declare</span> <span class="kt">double</span> <span class="vg">@foo</span><span class="p">()</span>
+
+<span class="k">declare</span> <span class="kt">double</span> <span class="vg">@bar</span><span class="p">()</span>
+
+<span class="k">define</span> <span class="kt">double</span> <span class="vg">@baz</span><span class="p">(</span><span class="kt">double</span> <span class="nv">%x</span><span class="p">)</span> <span class="p">{</span>
+<span class="nl">entry:</span>
+  <span class="nv">%ifcond</span> <span class="p">=</span> <span class="k">fcmp</span> <span class="k">one</span> <span class="kt">double</span> <span class="nv">%x</span><span class="p">,</span> <span class="m">0.000000e+00</span>
+  <span class="k">br</span> <span class="k">i1</span> <span class="nv">%ifcond</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%then</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%else</span>
+
+<span class="nl">then:</span>       <span class="c">; preds = %entry</span>
+  <span class="nv">%calltmp</span> <span class="p">=</span> <span class="k">call</span> <span class="kt">double</span> <span class="vg">@foo</span><span class="p">()</span>
+  <span class="k">br</span> <span class="kt">label</span> <span class="nv">%ifcont</span>
+
+<span class="nl">else:</span>       <span class="c">; preds = %entry</span>
+  <span class="nv">%calltmp1</span> <span class="p">=</span> <span class="k">call</span> <span class="kt">double</span> <span class="vg">@bar</span><span class="p">()</span>
+  <span class="k">br</span> <span class="kt">label</span> <span class="nv">%ifcont</span>
+
+<span class="nl">ifcont:</span>     <span class="c">; preds = %else, %then</span>
+  <span class="nv">%iftmp</span> <span class="p">=</span> <span class="k">phi</span> <span class="kt">double</span> <span class="p">[</span> <span class="nv">%calltmp</span><span class="p">,</span> <span class="nv">%then</span> <span class="p">],</span> <span class="p">[</span> <span class="nv">%calltmp1</span><span class="p">,</span> <span class="nv">%else</span> <span class="p">]</span>
+  <span class="k">ret</span> <span class="kt">double</span> <span class="nv">%iftmp</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>To visualize the control flow graph, you can use a nifty feature of the
+LLVM ‘<a class="reference external" href="http://llvm.org/cmds/opt.html">opt</a>‘ tool. If you put this LLVM
+IR into “t.ll” and run “<tt class="docutils literal"><span class="pre">llvm-as</span> <span class="pre"><</span> <span class="pre">t.ll</span> <span class="pre">|</span> <span class="pre">opt</span> <span class="pre">-analyze</span> <span class="pre">-view-cfg</span></tt>”, <a class="reference external" href="../ProgrammersManual.html#ViewGraph">a
+window will pop up</a> and you’ll
+see this graph:</p>
+<div class="figure align-center">
+<img alt="Example CFG" src="../_images/LangImpl5-cfg.png" />
+<p class="caption">Example CFG</p>
+</div>
+<p>Another way to get this is to call “<tt class="docutils literal"><span class="pre">F->viewCFG()</span></tt>” or
+“<tt class="docutils literal"><span class="pre">F->viewCFGOnly()</span></tt>” (where F is a “<tt class="docutils literal"><span class="pre">Function*</span></tt>”) either by
+inserting actual calls into the code and recompiling or by calling these
+in the debugger. LLVM has many nice features for visualizing various
+graphs.</p>
+<p>Getting back to the generated code, it is fairly simple: the entry block
+evaluates the conditional expression (“x” in our case here) and compares
+the result to 0.0 with the “<tt class="docutils literal"><span class="pre">fcmp</span> <span class="pre">one</span></tt>” instruction (‘one’ is “Ordered
+and Not Equal”). Based on the result of this expression, the code jumps
+to either the “then” or “else” blocks, which contain the expressions for
+the true/false cases.</p>
+<p>Once the then/else blocks are finished executing, they both branch back
+to the ‘ifcont’ block to execute the code that happens after the
+if/then/else. In this case the only thing left to do is to return to the
+caller of the function. The question then becomes: how does the code
+know which expression to return?</p>
+<p>The answer to this question involves an important SSA operation: the
+<a class="reference external" href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Phi
+operation</a>.
+If you’re not familiar with SSA, <a class="reference external" href="http://en.wikipedia.org/wiki/Static_single_assignment_form">the wikipedia
+article</a>
+is a good introduction and there are various other introductions to it
+available on your favorite search engine. The short version is that
+“execution” of the Phi operation requires “remembering” which block
+control came from. The Phi operation takes on the value corresponding to
+the input control block. In this case, if control comes in from the
+“then” block, it gets the value of “calltmp”. If control comes from the
+“else” block, it gets the value of “calltmp1”.</p>
+<p>At this point, you are probably starting to think “Oh no! This means my
+simple and elegant front-end will have to start generating SSA form in
+order to use LLVM!”. Fortunately, this is not the case, and we strongly
+advise <em>not</em> implementing an SSA construction algorithm in your
+front-end unless there is an amazingly good reason to do so. In
+practice, there are two sorts of values that float around in code
+written for your average imperative programming language that might need
+Phi nodes:</p>
+<ol class="arabic simple">
+<li>Code that involves user variables: <tt class="docutils literal"><span class="pre">x</span> <span class="pre">=</span> <span class="pre">1;</span> <span class="pre">x</span> <span class="pre">=</span> <span class="pre">x</span> <span class="pre">+</span> <span class="pre">1;</span></tt></li>
+<li>Values that are implicit in the structure of your AST, such as the
+Phi node in this case.</li>
+</ol>
+<p>In <a class="reference external" href="LangImpl7.html">Chapter 7</a> of this tutorial (“mutable variables”),
+we’ll talk about #1 in depth. For now, just believe me that you don’t
+need SSA construction to handle this case. For #2, you have the choice
+of using the techniques that we will describe for #1, or you can insert
+Phi nodes directly, if convenient. In this case, it is really
+easy to generate the Phi node, so we choose to do it directly.</p>
+<p>Okay, enough of the motivation and overview, lets generate code!</p>
+</div>
+<div class="section" id="code-generation-for-if-then-else">
+<h3><a class="toc-backref" href="#id7">5.2.5. Code Generation for If/Then/Else</a><a class="headerlink" href="#code-generation-for-if-then-else" title="Permalink to this headline">¶</a></h3>
+<p>In order to generate code for this, we implement the <tt class="docutils literal"><span class="pre">Codegen</span></tt> method
+for <tt class="docutils literal"><span class="pre">IfExprAST</span></tt>:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">Value</span> <span class="o">*</span><span class="n">IfExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">CondV</span> <span class="o">=</span> <span class="n">Cond</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CondV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Convert condition to a bool by comparing equal to 0.0.</span>
+  <span class="n">CondV</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpONE</span><span class="p">(</span><span class="n">CondV</span><span class="p">,</span>
+                              <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">)),</span>
+                                <span class="s">"ifcond"</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>This code is straightforward and similar to what we saw before. We emit
+the expression for the condition, then compare that value to zero to get
+a truth value as a 1-bit (bool) value.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+
+<span class="c1">// Create blocks for the then and else cases.  Insert the 'then' block at the</span>
+<span class="c1">// end of the function.</span>
+<span class="n">BasicBlock</span> <span class="o">*</span><span class="n">ThenBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"then"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+<span class="n">BasicBlock</span> <span class="o">*</span><span class="n">ElseBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"else"</span><span class="p">);</span>
+<span class="n">BasicBlock</span> <span class="o">*</span><span class="n">MergeBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"ifcont"</span><span class="p">);</span>
+
+<span class="n">Builder</span><span class="p">.</span><span class="n">CreateCondBr</span><span class="p">(</span><span class="n">CondV</span><span class="p">,</span> <span class="n">ThenBB</span><span class="p">,</span> <span class="n">ElseBB</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>This code creates the basic blocks that are related to the if/then/else
+statement, and correspond directly to the blocks in the example above.
+The first line gets the current Function object that is being built. It
+gets this by asking the builder for the current BasicBlock, and asking
+that block for its “parent” (the function it is currently embedded
+into).</p>
+<p>Once it has that, it creates three blocks. Note that it passes
+“TheFunction” into the constructor for the “then” block. This causes the
+constructor to automatically insert the new block into the end of the
+specified function. The other two blocks are created, but aren’t yet
+inserted into the function.</p>
+<p>Once the blocks are created, we can emit the conditional branch that
+chooses between them. Note that creating new blocks does not implicitly
+affect the IRBuilder, so it is still inserting into the block that the
+condition went into. Also note that it is creating a branch to the
+“then” block and the “else” block, even though the “else” block isn’t
+inserted into the function yet. This is all ok: it is the standard way
+that LLVM supports forward references.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Emit then value.</span>
+<span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">ThenBB</span><span class="p">);</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">ThenV</span> <span class="o">=</span> <span class="n">Then</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">ThenV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+<span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+<span class="c1">// Codegen of 'Then' can change the current block, update ThenBB for the PHI.</span>
+<span class="n">ThenBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+</pre></div>
+</div>
+<p>After the conditional branch is inserted, we move the builder to start
+inserting into the “then” block. Strictly speaking, this call moves the
+insertion point to be at the end of the specified block. However, since
+the “then” block is empty, it also starts out by inserting at the
+beginning of the block. :)</p>
+<p>Once the insertion point is set, we recursively codegen the “then”
+expression from the AST. To finish off the “then” block, we create an
+unconditional branch to the merge block. One interesting (and very
+important) aspect of the LLVM IR is that it <a class="reference external" href="../LangRef.html#functionstructure">requires all basic blocks
+to be “terminated”</a> with a <a class="reference external" href="../LangRef.html#terminators">control
+flow instruction</a> such as return or
+branch. This means that all control flow, <em>including fall throughs</em> must
+be made explicit in the LLVM IR. If you violate this rule, the verifier
+will emit an error.</p>
+<p>The final line here is quite subtle, but is very important. The basic
+issue is that when we create the Phi node in the merge block, we need to
+set up the block/value pairs that indicate how the Phi will work.
+Importantly, the Phi node expects to have an entry for each predecessor
+of the block in the CFG. Why then, are we getting the current block when
+we just set it to ThenBB 5 lines above? The problem is that the “Then”
+expression may actually itself change the block that the Builder is
+emitting into if, for example, it contains a nested “if/then/else”
+expression. Because calling Codegen recursively could arbitrarily change
+the notion of the current block, we are required to get an up-to-date
+value for code that will set up the Phi node.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Emit else block.</span>
+<span class="n">TheFunction</span><span class="o">-></span><span class="n">getBasicBlockList</span><span class="p">().</span><span class="n">push_back</span><span class="p">(</span><span class="n">ElseBB</span><span class="p">);</span>
+<span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">ElseBB</span><span class="p">);</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">ElseV</span> <span class="o">=</span> <span class="n">Else</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">ElseV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+<span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+<span class="c1">// Codegen of 'Else' can change the current block, update ElseBB for the PHI.</span>
+<span class="n">ElseBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+</pre></div>
+</div>
+<p>Code generation for the ‘else’ block is basically identical to codegen
+for the ‘then’ block. The only significant difference is the first line,
+which adds the ‘else’ block to the function. Recall previously that the
+‘else’ block was created, but not added to the function. Now that the
+‘then’ and ‘else’ blocks are emitted, we can finish up with the merge
+code:</p>
+<div class="highlight-c++"><div class="highlight"><pre>  <span class="c1">// Emit merge block.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">getBasicBlockList</span><span class="p">().</span><span class="n">push_back</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="n">PHINode</span> <span class="o">*</span><span class="n">PN</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreatePHI</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="mi">2</span><span class="p">,</span>
+                                  <span class="s">"iftmp"</span><span class="p">);</span>
+
+  <span class="n">PN</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">ThenV</span><span class="p">,</span> <span class="n">ThenBB</span><span class="p">);</span>
+  <span class="n">PN</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">ElseV</span><span class="p">,</span> <span class="n">ElseBB</span><span class="p">);</span>
+  <span class="k">return</span> <span class="n">PN</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>The first two lines here are now familiar: the first adds the “merge”
+block to the Function object (it was previously floating, like the else
+block above). The second changes the insertion point so that newly
+created code will go into the “merge” block. Once that is done, we need
+to create the PHI node and set up the block/value pairs for the PHI.</p>
+<p>Finally, the CodeGen function returns the phi node as the value computed
+by the if/then/else expression. In our example above, this returned
+value will feed into the code for the top-level function, which will
+create the return instruction.</p>
+<p>Overall, we now have the ability to execute conditional code in
+Kaleidoscope. With this extension, Kaleidoscope is a fairly complete
+language that can calculate a wide variety of numeric functions. Next up
+we’ll add another useful expression that is familiar from non-functional
+languages...</p>
+</div>
+</div>
+<div class="section" id="for-loop-expression">
+<h2><a class="toc-backref" href="#id8">5.3. ‘for’ Loop Expression</a><a class="headerlink" href="#for-loop-expression" title="Permalink to this headline">¶</a></h2>
+<p>Now that we know how to add basic control flow constructs to the
+language, we have the tools to add more powerful things. Lets add
+something more aggressive, a ‘for’ expression:</p>
+<div class="highlight-python"><div class="highlight"><pre>extern putchard(char)
+def printstar(n)
+  for i = 1, i < n, 1.0 in
+    putchard(42);  # ascii 42 = '*'
+
+# print 100 '*' characters
+printstar(100);
+</pre></div>
+</div>
+<p>This expression defines a new variable (“i” in this case) which iterates
+from a starting value, while the condition (“i < n” in this case) is
+true, incrementing by an optional step value (“1.0” in this case). If
+the step value is omitted, it defaults to 1.0. While the loop is true,
+it executes its body expression. Because we don’t have anything better
+to return, we’ll just define the loop as always returning 0.0. In the
+future when we have mutable variables, it will get more useful.</p>
+<p>As before, lets talk about the changes that we need to Kaleidoscope to
+support this.</p>
+<div class="section" id="lexer-extensions-for-the-for-loop">
+<h3><a class="toc-backref" href="#id9">5.3.1. Lexer Extensions for the ‘for’ Loop</a><a class="headerlink" href="#lexer-extensions-for-the-for-loop" title="Permalink to this headline">¶</a></h3>
+<p>The lexer extensions are the same sort of thing as for if/then/else:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="p">...</span> <span class="n">in</span> <span class="k">enum</span> <span class="n">Token</span> <span class="p">...</span>
+<span class="c1">// control</span>
+<span class="n">tok_if</span> <span class="o">=</span> <span class="o">-</span><span class="mi">6</span><span class="p">,</span> <span class="n">tok_then</span> <span class="o">=</span> <span class="o">-</span><span class="mi">7</span><span class="p">,</span> <span class="n">tok_else</span> <span class="o">=</span> <span class="o">-</span><span class="mi">8</span><span class="p">,</span>
+<span class="n">tok_for</span> <span class="o">=</span> <span class="o">-</span><span class="mi">9</span><span class="p">,</span> <span class="n">tok_in</span> <span class="o">=</span> <span class="o">-</span><span class="mi">10</span>
+
+<span class="p">...</span> <span class="n">in</span> <span class="n">gettok</span> <span class="p">...</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"def"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_def</span><span class="p">;</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"extern"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_extern</span><span class="p">;</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"if"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_if</span><span class="p">;</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"then"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_then</span><span class="p">;</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"else"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_else</span><span class="p">;</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"for"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_for</span><span class="p">;</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"in"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_in</span><span class="p">;</span>
+<span class="k">return</span> <span class="n">tok_identifier</span><span class="p">;</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="ast-extensions-for-the-for-loop">
+<h3><a class="toc-backref" href="#id10">5.3.2. AST Extensions for the ‘for’ Loop</a><a class="headerlink" href="#ast-extensions-for-the-for-loop" title="Permalink to this headline">¶</a></h3>
+<p>The AST node is just as simple. It basically boils down to capturing the
+variable name and the constituent expressions in the node.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// ForExprAST - Expression class for for/in.</span>
+<span class="k">class</span> <span class="nc">ForExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">VarName</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Start</span><span class="p">,</span> <span class="o">*</span><span class="n">End</span><span class="p">,</span> <span class="o">*</span><span class="n">Step</span><span class="p">,</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+<span class="nl">public:</span>
+  <span class="n">ForExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">varname</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">start</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">end</span><span class="p">,</span>
+             <span class="n">ExprAST</span> <span class="o">*</span><span class="n">step</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span>
+    <span class="o">:</span> <span class="n">VarName</span><span class="p">(</span><span class="n">varname</span><span class="p">),</span> <span class="n">Start</span><span class="p">(</span><span class="n">start</span><span class="p">),</span> <span class="n">End</span><span class="p">(</span><span class="n">end</span><span class="p">),</span> <span class="n">Step</span><span class="p">(</span><span class="n">step</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="k">virtual</span> <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="parser-extensions-for-the-for-loop">
+<h3><a class="toc-backref" href="#id11">5.3.3. Parser Extensions for the ‘for’ Loop</a><a class="headerlink" href="#parser-extensions-for-the-for-loop" title="Permalink to this headline">¶</a></h3>
+<p>The parser code is also fairly standard. The only interesting thing here
+is handling of the optional step value. The parser code handles it by
+checking to see if the second comma is present. If not, it sets the step
+value to null in the AST node:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseForExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span>  <span class="c1">// eat the for.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected identifier after for"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span>  <span class="c1">// eat identifier.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'='</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected '=' after for"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>  <span class="c1">// eat '='.</span>
+
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Start</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Start</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected ',' after for start value"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">End</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">End</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// The step value is optional.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Step</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">','</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="n">Step</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Step</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_in</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected 'in' after for"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>  <span class="c1">// eat 'in'.</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Body</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">ForExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">,</span> <span class="n">Start</span><span class="p">,</span> <span class="n">End</span><span class="p">,</span> <span class="n">Step</span><span class="p">,</span> <span class="n">Body</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="llvm-ir-for-the-for-loop">
+<h3><a class="toc-backref" href="#id12">5.3.4. LLVM IR for the ‘for’ Loop</a><a class="headerlink" href="#llvm-ir-for-the-for-loop" title="Permalink to this headline">¶</a></h3>
+<p>Now we get to the good part: the LLVM IR we want to generate for this
+thing. With the simple example above, we get this LLVM IR (note that
+this dump is generated with optimizations disabled for clarity):</p>
+<div class="highlight-llvm"><div class="highlight"><pre><span class="k">declare</span> <span class="kt">double</span> <span class="vg">@putchard</span><span class="p">(</span><span class="kt">double</span><span class="p">)</span>
+
+<span class="k">define</span> <span class="kt">double</span> <span class="vg">@printstar</span><span class="p">(</span><span class="kt">double</span> <span class="nv">%n</span><span class="p">)</span> <span class="p">{</span>
+<span class="nl">entry:</span>
+  <span class="c">; initial value = 1.0 (inlined into phi)</span>
+  <span class="k">br</span> <span class="kt">label</span> <span class="nv">%loop</span>
+
+<span class="nl">loop:</span>       <span class="c">; preds = %loop, %entry</span>
+  <span class="nv">%i</span> <span class="p">=</span> <span class="k">phi</span> <span class="kt">double</span> <span class="p">[</span> <span class="m">1.000000e+00</span><span class="p">,</span> <span class="nv">%entry</span> <span class="p">],</span> <span class="p">[</span> <span class="nv">%nextvar</span><span class="p">,</span> <span class="nv">%loop</span> <span class="p">]</span>
+  <span class="c">; body</span>
+  <span class="nv">%calltmp</span> <span class="p">=</span> <span class="k">call</span> <span class="kt">double</span> <span class="vg">@putchard</span><span class="p">(</span><span class="kt">double</span> <span class="m">4.200000e+01</span><span class="p">)</span>
+  <span class="c">; increment</span>
+  <span class="nv">%nextvar</span> <span class="p">=</span> <span class="k">fadd</span> <span class="kt">double</span> <span class="nv">%i</span><span class="p">,</span> <span class="m">1.000000e+00</span>
+
+  <span class="c">; termination test</span>
+  <span class="nv">%cmptmp</span> <span class="p">=</span> <span class="k">fcmp</span> <span class="k">ult</span> <span class="kt">double</span> <span class="nv">%i</span><span class="p">,</span> <span class="nv">%n</span>
+  <span class="nv">%booltmp</span> <span class="p">=</span> <span class="k">uitofp</span> <span class="k">i1</span> <span class="nv">%cmptmp</span> <span class="k">to</span> <span class="kt">double</span>
+  <span class="nv">%loopcond</span> <span class="p">=</span> <span class="k">fcmp</span> <span class="k">one</span> <span class="kt">double</span> <span class="nv">%booltmp</span><span class="p">,</span> <span class="m">0.000000e+00</span>
+  <span class="k">br</span> <span class="k">i1</span> <span class="nv">%loopcond</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%loop</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%afterloop</span>
+
+<span class="nl">afterloop:</span>      <span class="c">; preds = %loop</span>
+  <span class="c">; loop always returns 0.0</span>
+  <span class="k">ret</span> <span class="kt">double</span> <span class="m">0.000000e+00</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>This loop contains all the same constructs we saw before: a phi node,
+several expressions, and some basic blocks. Lets see how this fits
+together.</p>
+</div>
+<div class="section" id="code-generation-for-the-for-loop">
+<h3><a class="toc-backref" href="#id13">5.3.5. Code Generation for the ‘for’ Loop</a><a class="headerlink" href="#code-generation-for-the-for-loop" title="Permalink to this headline">¶</a></h3>
+<p>The first part of Codegen is very simple: we just output the start
+expression for the loop value:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">Value</span> <span class="o">*</span><span class="n">ForExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Emit the start code first, without 'variable' in scope.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">StartVal</span> <span class="o">=</span> <span class="n">Start</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">StartVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>With this out of the way, the next step is to set up the LLVM basic
+block for the start of the loop body. In the case above, the whole loop
+body is one block, but remember that the body code itself could consist
+of multiple blocks (e.g. if it contains an if/then/else or a for/in
+expression).</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Make the new basic block for the loop header, inserting after current</span>
+<span class="c1">// block.</span>
+<span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+<span class="n">BasicBlock</span> <span class="o">*</span><span class="n">PreheaderBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+<span class="n">BasicBlock</span> <span class="o">*</span><span class="n">LoopBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"loop"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+
+<span class="c1">// Insert an explicit fall through from the current block to the LoopBB.</span>
+<span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">LoopBB</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>This code is similar to what we saw for if/then/else. Because we will
+need it to create the Phi node, we remember the block that falls through
+into the loop. Once we have that, we create the actual block that starts
+the loop and create an unconditional branch for the fall-through between
+the two blocks.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Start insertion in LoopBB.</span>
+<span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">LoopBB</span><span class="p">);</span>
+
+<span class="c1">// Start the PHI node with an entry for Start.</span>
+<span class="n">PHINode</span> <span class="o">*</span><span class="n">Variable</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreatePHI</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="mi">2</span><span class="p">,</span> <span class="n">VarName</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+<span class="n">Variable</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">StartVal</span><span class="p">,</span> <span class="n">PreheaderBB</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>Now that the “preheader” for the loop is set up, we switch to emitting
+code for the loop body. To begin with, we move the insertion point and
+create the PHI node for the loop induction variable. Since we already
+know the incoming value for the starting value, we add it to the Phi
+node. Note that the Phi will eventually get a second value for the
+backedge, but we can’t set it up yet (because it doesn’t exist!).</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Within the loop, the variable is defined equal to the PHI node.  If it</span>
+<span class="c1">// shadows an existing variable, we have to restore it, so save it now.</span>
+<span class="n">Value</span> <span class="o">*</span><span class="n">OldVal</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">];</span>
+<span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">Variable</span><span class="p">;</span>
+
+<span class="c1">// Emit the body of the loop.  This, like any other expr, can change the</span>
+<span class="c1">// current BB.  Note that we ignore the value computed by the body, but don't</span>
+<span class="c1">// allow an error.</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">()</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>Now the code starts to get more interesting. Our ‘for’ loop introduces a
+new variable to the symbol table. This means that our symbol table can
+now contain either function arguments or loop variables. To handle this,
+before we codegen the body of the loop, we add the loop variable as the
+current value for its name. Note that it is possible that there is a
+variable of the same name in the outer scope. It would be easy to make
+this an error (emit an error and return null if there is already an
+entry for VarName) but we choose to allow shadowing of variables. In
+order to handle this correctly, we remember the Value that we are
+potentially shadowing in <tt class="docutils literal"><span class="pre">OldVal</span></tt> (which will be null if there is no
+shadowed variable).</p>
+<p>Once the loop variable is set into the symbol table, the code
+recursively codegen’s the body. This allows the body to use the loop
+variable: any references to it will naturally find it in the symbol
+table.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Emit the step value.</span>
+<span class="n">Value</span> <span class="o">*</span><span class="n">StepVal</span><span class="p">;</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">Step</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">StepVal</span> <span class="o">=</span> <span class="n">Step</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">StepVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+  <span class="c1">// If not specified, use 1.0.</span>
+  <span class="n">StepVal</span> <span class="o">=</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">1.0</span><span class="p">));</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">NextVar</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFAdd</span><span class="p">(</span><span class="n">Variable</span><span class="p">,</span> <span class="n">StepVal</span><span class="p">,</span> <span class="s">"nextvar"</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>Now that the body is emitted, we compute the next value of the iteration
+variable by adding the step value, or 1.0 if it isn’t present.
+‘<tt class="docutils literal"><span class="pre">NextVar</span></tt>‘ will be the value of the loop variable on the next
+iteration of the loop.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Compute the end condition.</span>
+<span class="n">Value</span> <span class="o">*</span><span class="n">EndCond</span> <span class="o">=</span> <span class="n">End</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">EndCond</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="n">EndCond</span><span class="p">;</span>
+
+<span class="c1">// Convert condition to a bool by comparing equal to 0.0.</span>
+<span class="n">EndCond</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpONE</span><span class="p">(</span><span class="n">EndCond</span><span class="p">,</span>
+                            <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">)),</span>
+                                <span class="s">"loopcond"</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>Finally, we evaluate the exit value of the loop, to determine whether
+the loop should exit. This mirrors the condition evaluation for the
+if/then/else statement.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Create the "after loop" block and insert it.</span>
+<span class="n">BasicBlock</span> <span class="o">*</span><span class="n">LoopEndBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+<span class="n">BasicBlock</span> <span class="o">*</span><span class="n">AfterBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"afterloop"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+
+<span class="c1">// Insert the conditional branch into the end of LoopEndBB.</span>
+<span class="n">Builder</span><span class="p">.</span><span class="n">CreateCondBr</span><span class="p">(</span><span class="n">EndCond</span><span class="p">,</span> <span class="n">LoopBB</span><span class="p">,</span> <span class="n">AfterBB</span><span class="p">);</span>
+
+<span class="c1">// Any new code will be inserted in AfterBB.</span>
+<span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">AfterBB</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>With the code for the body of the loop complete, we just need to finish
+up the control flow for it. This code remembers the end block (for the
+phi node), then creates the block for the loop exit (“afterloop”). Based
+on the value of the exit condition, it creates a conditional branch that
+chooses between executing the loop again and exiting the loop. Any
+future code is emitted in the “afterloop” block, so it sets the
+insertion position to it.</p>
+<div class="highlight-c++"><div class="highlight"><pre>  <span class="c1">// Add a new entry to the PHI node for the backedge.</span>
+  <span class="n">Variable</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">NextVar</span><span class="p">,</span> <span class="n">LoopEndBB</span><span class="p">);</span>
+
+  <span class="c1">// Restore the unshadowed variable.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">OldVal</span><span class="p">)</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">OldVal</span><span class="p">;</span>
+  <span class="k">else</span>
+    <span class="n">NamedValues</span><span class="p">.</span><span class="n">erase</span><span class="p">(</span><span class="n">VarName</span><span class="p">);</span>
+
+  <span class="c1">// for expr always returns 0.0.</span>
+  <span class="k">return</span> <span class="n">Constant</span><span class="o">::</span><span class="n">getNullValue</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()));</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>The final code handles various cleanups: now that we have the “NextVar”
+value, we can add the incoming value to the loop PHI node. After that,
+we remove the loop variable from the symbol table, so that it isn’t in
+scope after the for loop. Finally, code generation of the for loop
+always returns 0.0, so that is what we return from
+<tt class="docutils literal"><span class="pre">ForExprAST::Codegen</span></tt>.</p>
+<p>With this, we conclude the “adding control flow to Kaleidoscope” chapter
+of the tutorial. In this chapter we added two control flow constructs,
+and used them to motivate a couple of aspects of the LLVM IR that are
+important for front-end implementors to know. In the next chapter of our
+saga, we will get a bit crazier and add <a class="reference external" href="LangImpl6.html">user-defined
+operators</a> to our poor innocent language.</p>
+</div>
+</div>
+<div class="section" id="full-code-listing">
+<h2><a class="toc-backref" href="#id14">5.4. Full Code Listing</a><a class="headerlink" href="#full-code-listing" title="Permalink to this headline">¶</a></h2>
+<p>Here is the complete code listing for our running example, enhanced with
+the if/then/else and for expressions.. To build this example, use:</p>
+<div class="highlight-bash"><div class="highlight"><pre><span class="c"># Compile</span>
+clang++ -g toy.cpp <span class="sb">`</span>llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native<span class="sb">`</span> -O3 -o toy
+<span class="c"># Run</span>
+./toy
+</pre></div>
+</div>
+<p>Here is the code:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include "llvm/ADT/STLExtras.h"</span>
+<span class="cp">#include "llvm/Analysis/Passes.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/ExecutionEngine.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/MCJIT.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/SectionMemoryManager.h"</span>
+<span class="cp">#include "llvm/IR/DataLayout.h"</span>
+<span class="cp">#include "llvm/IR/DerivedTypes.h"</span>
+<span class="cp">#include "llvm/IR/IRBuilder.h"</span>
+<span class="cp">#include "llvm/IR/LLVMContext.h"</span>
+<span class="cp">#include "llvm/IR/LegacyPassManager.h"</span>
+<span class="cp">#include "llvm/IR/Module.h"</span>
+<span class="cp">#include "llvm/IR/Verifier.h"</span>
+<span class="cp">#include "llvm/Support/TargetSelect.h"</span>
+<span class="cp">#include "llvm/Transforms/Scalar.h"</span>
+<span class="cp">#include <cctype></span>
+<span class="cp">#include <cstdio></span>
+<span class="cp">#include <map></span>
+<span class="cp">#include <string></span>
+<span class="cp">#include <vector></span>
+<span class="k">using</span> <span class="k">namespace</span> <span class="n">llvm</span><span class="p">;</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Lexer</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">// The lexer returns tokens [0-255] if it is an unknown character, otherwise one</span>
+<span class="c1">// of these for known things.</span>
+<span class="k">enum</span> <span class="n">Token</span> <span class="p">{</span>
+  <span class="n">tok_eof</span> <span class="o">=</span> <span class="o">-</span><span class="mi">1</span><span class="p">,</span>
+
+  <span class="c1">// commands</span>
+  <span class="n">tok_def</span> <span class="o">=</span> <span class="o">-</span><span class="mi">2</span><span class="p">,</span>
+  <span class="n">tok_extern</span> <span class="o">=</span> <span class="o">-</span><span class="mi">3</span><span class="p">,</span>
+
+  <span class="c1">// primary</span>
+  <span class="n">tok_identifier</span> <span class="o">=</span> <span class="o">-</span><span class="mi">4</span><span class="p">,</span>
+  <span class="n">tok_number</span> <span class="o">=</span> <span class="o">-</span><span class="mi">5</span><span class="p">,</span>
+
+  <span class="c1">// control</span>
+  <span class="n">tok_if</span> <span class="o">=</span> <span class="o">-</span><span class="mi">6</span><span class="p">,</span>
+  <span class="n">tok_then</span> <span class="o">=</span> <span class="o">-</span><span class="mi">7</span><span class="p">,</span>
+  <span class="n">tok_else</span> <span class="o">=</span> <span class="o">-</span><span class="mi">8</span><span class="p">,</span>
+  <span class="n">tok_for</span> <span class="o">=</span> <span class="o">-</span><span class="mi">9</span><span class="p">,</span>
+  <span class="n">tok_in</span> <span class="o">=</span> <span class="o">-</span><span class="mi">10</span>
+<span class="p">};</span>
+
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdentifierStr</span><span class="p">;</span> <span class="c1">// Filled in if tok_identifier</span>
+<span class="k">static</span> <span class="kt">double</span> <span class="n">NumVal</span><span class="p">;</span>             <span class="c1">// Filled in if tok_number</span>
+
+<span class="c1">/// gettok - Return the next token from standard input.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">gettok</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">static</span> <span class="kt">int</span> <span class="n">LastChar</span> <span class="o">=</span> <span class="sc">' '</span><span class="p">;</span>
+
+  <span class="c1">// Skip any whitespace.</span>
+  <span class="k">while</span> <span class="p">(</span><span class="n">isspace</span><span class="p">(</span><span class="n">LastChar</span><span class="p">))</span>
+    <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">isalpha</span><span class="p">(</span><span class="n">LastChar</span><span class="p">))</span> <span class="p">{</span> <span class="c1">// identifier: [a-zA-Z][a-zA-Z0-9]*</span>
+    <span class="n">IdentifierStr</span> <span class="o">=</span> <span class="n">LastChar</span><span class="p">;</span>
+    <span class="k">while</span> <span class="p">(</span><span class="n">isalnum</span><span class="p">((</span><span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">())))</span>
+      <span class="n">IdentifierStr</span> <span class="o">+=</span> <span class="n">LastChar</span><span class="p">;</span>
+
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"def"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_def</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"extern"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_extern</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"if"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_if</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"then"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_then</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"else"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_else</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"for"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_for</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"in"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_in</span><span class="p">;</span>
+    <span class="k">return</span> <span class="n">tok_identifier</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">isdigit</span><span class="p">(</span><span class="n">LastChar</span><span class="p">)</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">)</span> <span class="p">{</span> <span class="c1">// Number: [0-9.]+</span>
+    <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">NumStr</span><span class="p">;</span>
+    <span class="k">do</span> <span class="p">{</span>
+      <span class="n">NumStr</span> <span class="o">+=</span> <span class="n">LastChar</span><span class="p">;</span>
+      <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+    <span class="p">}</span> <span class="k">while</span> <span class="p">(</span><span class="n">isdigit</span><span class="p">(</span><span class="n">LastChar</span><span class="p">)</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">);</span>
+
+    <span class="n">NumVal</span> <span class="o">=</span> <span class="n">strtod</span><span class="p">(</span><span class="n">NumStr</span><span class="p">.</span><span class="n">c_str</span><span class="p">(),</span> <span class="mi">0</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">tok_number</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'#'</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Comment until end of line.</span>
+    <span class="k">do</span>
+      <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+    <span class="k">while</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">!=</span> <span class="n">EOF</span> <span class="o">&&</span> <span class="n">LastChar</span> <span class="o">!=</span> <span class="sc">'\n'</span> <span class="o">&&</span> <span class="n">LastChar</span> <span class="o">!=</span> <span class="sc">'\r'</span><span class="p">);</span>
+
+    <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">!=</span> <span class="n">EOF</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">gettok</span><span class="p">();</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Check for end of file.  Don't eat the EOF.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="n">EOF</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">tok_eof</span><span class="p">;</span>
+
+  <span class="c1">// Otherwise, just return the character as its ascii value.</span>
+  <span class="kt">int</span> <span class="n">ThisChar</span> <span class="o">=</span> <span class="n">LastChar</span><span class="p">;</span>
+  <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+  <span class="k">return</span> <span class="n">ThisChar</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Abstract Syntax Tree (aka Parse Tree)</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="k">namespace</span> <span class="p">{</span>
+<span class="c1">/// ExprAST - Base class for all expression nodes.</span>
+<span class="k">class</span> <span class="nc">ExprAST</span> <span class="p">{</span>
+<span class="nl">public:</span>
+  <span class="k">virtual</span> <span class="o">~</span><span class="n">ExprAST</span><span class="p">()</span> <span class="p">{}</span>
+  <span class="k">virtual</span> <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// NumberExprAST - Expression class for numeric literals like "1.0".</span>
+<span class="k">class</span> <span class="nc">NumberExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">double</span> <span class="n">Val</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">NumberExprAST</span><span class="p">(</span><span class="kt">double</span> <span class="n">val</span><span class="p">)</span> <span class="o">:</span> <span class="n">Val</span><span class="p">(</span><span class="n">val</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// VariableExprAST - Expression class for referencing a variable, like "a".</span>
+<span class="k">class</span> <span class="nc">VariableExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">VariableExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">name</span><span class="p">)</span> <span class="o">:</span> <span class="n">Name</span><span class="p">(</span><span class="n">name</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// BinaryExprAST - Expression class for a binary operator.</span>
+<span class="k">class</span> <span class="nc">BinaryExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">char</span> <span class="n">Op</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span><span class="p">,</span> <span class="o">*</span><span class="n">RHS</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">BinaryExprAST</span><span class="p">(</span><span class="kt">char</span> <span class="n">op</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">lhs</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">rhs</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Op</span><span class="p">(</span><span class="n">op</span><span class="p">),</span> <span class="n">LHS</span><span class="p">(</span><span class="n">lhs</span><span class="p">),</span> <span class="n">RHS</span><span class="p">(</span><span class="n">rhs</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// CallExprAST - Expression class for function calls.</span>
+<span class="k">class</span> <span class="nc">CallExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Callee</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="n">Args</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">CallExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">callee</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="o">&</span><span class="n">args</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Callee</span><span class="p">(</span><span class="n">callee</span><span class="p">),</span> <span class="n">Args</span><span class="p">(</span><span class="n">args</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// IfExprAST - Expression class for if/then/else.</span>
+<span class="k">class</span> <span class="nc">IfExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Cond</span><span class="p">,</span> <span class="o">*</span><span class="n">Then</span><span class="p">,</span> <span class="o">*</span><span class="n">Else</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">IfExprAST</span><span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">cond</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">then</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">_else</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Cond</span><span class="p">(</span><span class="n">cond</span><span class="p">),</span> <span class="n">Then</span><span class="p">(</span><span class="n">then</span><span class="p">),</span> <span class="n">Else</span><span class="p">(</span><span class="n">_else</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// ForExprAST - Expression class for for/in.</span>
+<span class="k">class</span> <span class="nc">ForExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">VarName</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Start</span><span class="p">,</span> <span class="o">*</span><span class="n">End</span><span class="p">,</span> <span class="o">*</span><span class="n">Step</span><span class="p">,</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">ForExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">varname</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">start</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">end</span><span class="p">,</span>
+             <span class="n">ExprAST</span> <span class="o">*</span><span class="n">step</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">VarName</span><span class="p">(</span><span class="n">varname</span><span class="p">),</span> <span class="n">Start</span><span class="p">(</span><span class="n">start</span><span class="p">),</span> <span class="n">End</span><span class="p">(</span><span class="n">end</span><span class="p">),</span> <span class="n">Step</span><span class="p">(</span><span class="n">step</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// PrototypeAST - This class represents the "prototype" for a function,</span>
+<span class="c1">/// which captures its name, and its argument names (thus implicitly the number</span>
+<span class="c1">/// of arguments the function takes).</span>
+<span class="k">class</span> <span class="nc">PrototypeAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">Args</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">PrototypeAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">name</span><span class="p">,</span> <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="o">&</span><span class="n">args</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Name</span><span class="p">(</span><span class="n">name</span><span class="p">),</span> <span class="n">Args</span><span class="p">(</span><span class="n">args</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+
+<span class="c1">/// FunctionAST - This class represents a function definition itself.</span>
+<span class="k">class</span> <span class="nc">FunctionAST</span> <span class="p">{</span>
+  <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">FunctionAST</span><span class="p">(</span><span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">proto</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span> <span class="o">:</span> <span class="n">Proto</span><span class="p">(</span><span class="n">proto</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+<span class="p">}</span> <span class="c1">// end anonymous namespace</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Parser</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">/// CurTok/getNextToken - Provide a simple token buffer.  CurTok is the current</span>
+<span class="c1">/// token the parser is looking at.  getNextToken reads another token from the</span>
+<span class="c1">/// lexer and updates CurTok with its results.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="n">CurTok</span><span class="p">;</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">getNextToken</span><span class="p">()</span> <span class="p">{</span> <span class="k">return</span> <span class="n">CurTok</span> <span class="o">=</span> <span class="n">gettok</span><span class="p">();</span> <span class="p">}</span>
+
+<span class="c1">/// BinopPrecedence - This holds the precedence for each binary operator that is</span>
+<span class="c1">/// defined.</span>
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="kt">char</span><span class="p">,</span> <span class="kt">int</span><span class="o">></span> <span class="n">BinopPrecedence</span><span class="p">;</span>
+
+<span class="c1">/// GetTokPrecedence - Get the precedence of the pending binary operator token.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">GetTokPrecedence</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+    <span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
+
+  <span class="c1">// Make sure it's a declared binop.</span>
+  <span class="kt">int</span> <span class="n">TokPrec</span> <span class="o">=</span> <span class="n">BinopPrecedence</span><span class="p">[</span><span class="n">CurTok</span><span class="p">];</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><=</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
+  <span class="k">return</span> <span class="n">TokPrec</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// Error* - These are little helper functions for error handling.</span>
+<span class="n">ExprAST</span> <span class="o">*</span><span class="nf">Error</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Error: %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+<span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ErrorP</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+<span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ErrorF</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseExpression</span><span class="p">();</span>
+
+<span class="c1">/// identifierexpr</span>
+<span class="c1">///   ::= identifier</span>
+<span class="c1">///   ::= identifier '(' expression* ')'</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseIdentifierExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat identifier.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'('</span><span class="p">)</span> <span class="c1">// Simple variable ref.</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">VariableExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">);</span>
+
+  <span class="c1">// Call.</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat (</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="n">Args</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Arg</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+      <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Arg</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+      <span class="n">Args</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">Arg</span><span class="p">);</span>
+
+      <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">')'</span><span class="p">)</span>
+        <span class="k">break</span><span class="p">;</span>
+
+      <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span>
+        <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"Expected ')' or ',' in argument list"</span><span class="p">);</span>
+      <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Eat the ')'.</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">CallExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">,</span> <span class="n">Args</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// numberexpr ::= number</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseNumberExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Result</span> <span class="o">=</span> <span class="k">new</span> <span class="n">NumberExprAST</span><span class="p">(</span><span class="n">NumVal</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// consume the number</span>
+  <span class="k">return</span> <span class="n">Result</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// parenexpr ::= '(' expression ')'</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseParenExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat (.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">V</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">V</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected ')'"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat ).</span>
+  <span class="k">return</span> <span class="n">V</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// ifexpr ::= 'if' expression 'then' expression 'else' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseIfExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the if.</span>
+
+  <span class="c1">// condition.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Cond</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Cond</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_then</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected then"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the then</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Then</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Then</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_else</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected else"</span><span class="p">);</span>
+
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Else</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Else</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">IfExprAST</span><span class="p">(</span><span class="n">Cond</span><span class="p">,</span> <span class="n">Then</span><span class="p">,</span> <span class="n">Else</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseForExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the for.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected identifier after for"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat identifier.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'='</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected '=' after for"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat '='.</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Start</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Start</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected ',' after for start value"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">End</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">End</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// The step value is optional.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Step</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">','</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="n">Step</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Step</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_in</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected 'in' after for"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat 'in'.</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Body</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">ForExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">,</span> <span class="n">Start</span><span class="p">,</span> <span class="n">End</span><span class="p">,</span> <span class="n">Step</span><span class="p">,</span> <span class="n">Body</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// primary</span>
+<span class="c1">///   ::= identifierexpr</span>
+<span class="c1">///   ::= numberexpr</span>
+<span class="c1">///   ::= parenexpr</span>
+<span class="c1">///   ::= ifexpr</span>
+<span class="c1">///   ::= forexpr</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParsePrimary</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="nl">default:</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"unknown token when expecting an expression"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>:
+    <span class="k">return</span> <span class="n">ParseIdentifierExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_number</span>:
+    <span class="k">return</span> <span class="n">ParseNumberExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="sc">'('</span>:
+    <span class="k">return</span> <span class="n">ParseParenExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_if</span>:
+    <span class="k">return</span> <span class="n">ParseIfExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_for</span>:
+    <span class="k">return</span> <span class="n">ParseForExpr</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// binoprhs</span>
+<span class="c1">///   ::= ('+' primary)*</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseBinOpRHS</span><span class="p">(</span><span class="kt">int</span> <span class="n">ExprPrec</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span><span class="p">)</span> <span class="p">{</span>
+  <span class="c1">// If this is a binop, find its precedence.</span>
+  <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+    <span class="kt">int</span> <span class="n">TokPrec</span> <span class="o">=</span> <span class="n">GetTokPrecedence</span><span class="p">();</span>
+
+    <span class="c1">// If this is a binop that binds at least as tightly as the current binop,</span>
+    <span class="c1">// consume it, otherwise we are done.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><</span> <span class="n">ExprPrec</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">LHS</span><span class="p">;</span>
+
+    <span class="c1">// Okay, we know this is a binop.</span>
+    <span class="kt">int</span> <span class="n">BinOp</span> <span class="o">=</span> <span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat binop</span>
+
+    <span class="c1">// Parse the primary expression after the binary operator.</span>
+    <span class="n">ExprAST</span> <span class="o">*</span><span class="n">RHS</span> <span class="o">=</span> <span class="n">ParsePrimary</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">RHS</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+    <span class="c1">// If BinOp binds less tightly with RHS than the operator after RHS, let</span>
+    <span class="c1">// the pending operator take RHS as its LHS.</span>
+    <span class="kt">int</span> <span class="n">NextPrec</span> <span class="o">=</span> <span class="n">GetTokPrecedence</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><</span> <span class="n">NextPrec</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">RHS</span> <span class="o">=</span> <span class="n">ParseBinOpRHS</span><span class="p">(</span><span class="n">TokPrec</span> <span class="o">+</span> <span class="mi">1</span><span class="p">,</span> <span class="n">RHS</span><span class="p">);</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">RHS</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+
+    <span class="c1">// Merge LHS/RHS.</span>
+    <span class="n">LHS</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BinaryExprAST</span><span class="p">(</span><span class="n">BinOp</span><span class="p">,</span> <span class="n">LHS</span><span class="p">,</span> <span class="n">RHS</span><span class="p">);</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// expression</span>
+<span class="c1">///   ::= primary binoprhs</span>
+<span class="c1">///</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseExpression</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span> <span class="o">=</span> <span class="n">ParsePrimary</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">LHS</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="n">ParseBinOpRHS</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">LHS</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// prototype</span>
+<span class="c1">///   ::= id '(' id* ')'</span>
+<span class="k">static</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ParsePrototype</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected function name in prototype"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">FnName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'('</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected '(' in prototype"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">ArgNames</span><span class="p">;</span>
+  <span class="k">while</span> <span class="p">(</span><span class="n">getNextToken</span><span class="p">()</span> <span class="o">==</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="n">ArgNames</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">IdentifierStr</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected ')' in prototype"</span><span class="p">);</span>
+
+  <span class="c1">// success.</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat ')'.</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">PrototypeAST</span><span class="p">(</span><span class="n">FnName</span><span class="p">,</span> <span class="n">ArgNames</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// definition ::= 'def' prototype expression</span>
+<span class="k">static</span> <span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ParseDefinition</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat def.</span>
+  <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span> <span class="o">=</span> <span class="n">ParsePrototype</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Proto</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">E</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">())</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">FunctionAST</span><span class="p">(</span><span class="n">Proto</span><span class="p">,</span> <span class="n">E</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// toplevelexpr ::= expression</span>
+<span class="k">static</span> <span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ParseTopLevelExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">E</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">())</span> <span class="p">{</span>
+    <span class="c1">// Make an anonymous proto.</span>
+    <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span> <span class="o">=</span> <span class="k">new</span> <span class="n">PrototypeAST</span><span class="p">(</span><span class="s">""</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="p">());</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">FunctionAST</span><span class="p">(</span><span class="n">Proto</span><span class="p">,</span> <span class="n">E</span><span class="p">);</span>
+  <span class="p">}</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// external ::= 'extern' prototype</span>
+<span class="k">static</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ParseExtern</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat extern.</span>
+  <span class="k">return</span> <span class="n">ParsePrototype</span><span class="p">();</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Code Generation</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="k">static</span> <span class="n">Module</span> <span class="o">*</span><span class="n">TheModule</span><span class="p">;</span>
+<span class="k">static</span> <span class="n">IRBuilder</span><span class="o"><></span> <span class="n">Builder</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">());</span>
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">Value</span> <span class="o">*></span> <span class="n">NamedValues</span><span class="p">;</span>
+<span class="k">static</span> <span class="n">legacy</span><span class="o">::</span><span class="n">FunctionPassManager</span> <span class="o">*</span><span class="n">TheFPM</span><span class="p">;</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="nf">ErrorV</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">NumberExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">return</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="n">Val</span><span class="p">));</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">VariableExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Look this variable up in the function.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">V</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">Name</span><span class="p">];</span>
+  <span class="k">return</span> <span class="n">V</span> <span class="o">?</span> <span class="n">V</span> <span class="o">:</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown variable name"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">BinaryExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">L</span> <span class="o">=</span> <span class="n">LHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">R</span> <span class="o">=</span> <span class="n">RHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">L</span> <span class="o">==</span> <span class="mi">0</span> <span class="o">||</span> <span class="n">R</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">switch</span> <span class="p">(</span><span class="n">Op</span><span class="p">)</span> <span class="p">{</span>
+  <span class="k">case</span> <span class="sc">'+'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFAdd</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"addtmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'-'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFSub</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"subtmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'*'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFMul</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"multmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'<'</span>:
+    <span class="n">L</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpULT</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"cmptmp"</span><span class="p">);</span>
+    <span class="c1">// Convert bool 0/1 to double 0.0 or 1.0</span>
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateUIToFP</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span>
+                                <span class="s">"booltmp"</span><span class="p">);</span>
+  <span class="nl">default:</span>
+    <span class="k">return</span> <span class="nf">ErrorV</span><span class="p">(</span><span class="s">"invalid binary operator"</span><span class="p">);</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">CallExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Look up the name in the global module table.</span>
+  <span class="n">Function</span> <span class="o">*</span><span class="n">CalleeF</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">Callee</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CalleeF</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown function referenced"</span><span class="p">);</span>
+
+  <span class="c1">// If argument mismatch error.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CalleeF</span><span class="o">-></span><span class="n">arg_size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">())</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Incorrect # arguments passed"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">Value</span> <span class="o">*></span> <span class="n">ArgsV</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">ArgsV</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">Args</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="o">-></span><span class="n">Codegen</span><span class="p">());</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">ArgsV</span><span class="p">.</span><span class="n">back</span><span class="p">()</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">CalleeF</span><span class="p">,</span> <span class="n">ArgsV</span><span class="p">,</span> <span class="s">"calltmp"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">IfExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">CondV</span> <span class="o">=</span> <span class="n">Cond</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CondV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Convert condition to a bool by comparing equal to 0.0.</span>
+  <span class="n">CondV</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpONE</span><span class="p">(</span>
+      <span class="n">CondV</span><span class="p">,</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">)),</span> <span class="s">"ifcond"</span><span class="p">);</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+
+  <span class="c1">// Create blocks for the then and else cases.  Insert the 'then' block at the</span>
+  <span class="c1">// end of the function.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">ThenBB</span> <span class="o">=</span>
+      <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"then"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">ElseBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"else"</span><span class="p">);</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">MergeBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"ifcont"</span><span class="p">);</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCondBr</span><span class="p">(</span><span class="n">CondV</span><span class="p">,</span> <span class="n">ThenBB</span><span class="p">,</span> <span class="n">ElseBB</span><span class="p">);</span>
+
+  <span class="c1">// Emit then value.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">ThenBB</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">ThenV</span> <span class="o">=</span> <span class="n">Then</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ThenV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="c1">// Codegen of 'Then' can change the current block, update ThenBB for the PHI.</span>
+  <span class="n">ThenBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+
+  <span class="c1">// Emit else block.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">getBasicBlockList</span><span class="p">().</span><span class="n">push_back</span><span class="p">(</span><span class="n">ElseBB</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">ElseBB</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">ElseV</span> <span class="o">=</span> <span class="n">Else</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ElseV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="c1">// Codegen of 'Else' can change the current block, update ElseBB for the PHI.</span>
+  <span class="n">ElseBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+
+  <span class="c1">// Emit merge block.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">getBasicBlockList</span><span class="p">().</span><span class="n">push_back</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="n">PHINode</span> <span class="o">*</span><span class="n">PN</span> <span class="o">=</span>
+      <span class="n">Builder</span><span class="p">.</span><span class="n">CreatePHI</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="mi">2</span><span class="p">,</span> <span class="s">"iftmp"</span><span class="p">);</span>
+
+  <span class="n">PN</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">ThenV</span><span class="p">,</span> <span class="n">ThenBB</span><span class="p">);</span>
+  <span class="n">PN</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">ElseV</span><span class="p">,</span> <span class="n">ElseBB</span><span class="p">);</span>
+  <span class="k">return</span> <span class="n">PN</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">ForExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Output this as:</span>
+  <span class="c1">//   ...</span>
+  <span class="c1">//   start = startexpr</span>
+  <span class="c1">//   goto loop</span>
+  <span class="c1">// loop:</span>
+  <span class="c1">//   variable = phi [start, loopheader], [nextvariable, loopend]</span>
+  <span class="c1">//   ...</span>
+  <span class="c1">//   bodyexpr</span>
+  <span class="c1">//   ...</span>
+  <span class="c1">// loopend:</span>
+  <span class="c1">//   step = stepexpr</span>
+  <span class="c1">//   nextvariable = variable + step</span>
+  <span class="c1">//   endcond = endexpr</span>
+  <span class="c1">//   br endcond, loop, endloop</span>
+  <span class="c1">// outloop:</span>
+
+  <span class="c1">// Emit the start code first, without 'variable' in scope.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">StartVal</span> <span class="o">=</span> <span class="n">Start</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">StartVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Make the new basic block for the loop header, inserting after current</span>
+  <span class="c1">// block.</span>
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">PreheaderBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">LoopBB</span> <span class="o">=</span>
+      <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"loop"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+
+  <span class="c1">// Insert an explicit fall through from the current block to the LoopBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">LoopBB</span><span class="p">);</span>
+
+  <span class="c1">// Start insertion in LoopBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">LoopBB</span><span class="p">);</span>
+
+  <span class="c1">// Start the PHI node with an entry for Start.</span>
+  <span class="n">PHINode</span> <span class="o">*</span><span class="n">Variable</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreatePHI</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span>
+                                        <span class="mi">2</span><span class="p">,</span> <span class="n">VarName</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+  <span class="n">Variable</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">StartVal</span><span class="p">,</span> <span class="n">PreheaderBB</span><span class="p">);</span>
+
+  <span class="c1">// Within the loop, the variable is defined equal to the PHI node.  If it</span>
+  <span class="c1">// shadows an existing variable, we have to restore it, so save it now.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">OldVal</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">];</span>
+  <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">Variable</span><span class="p">;</span>
+
+  <span class="c1">// Emit the body of the loop.  This, like any other expr, can change the</span>
+  <span class="c1">// current BB.  Note that we ignore the value computed by the body, but don't</span>
+  <span class="c1">// allow an error.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">()</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Emit the step value.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">StepVal</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Step</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">StepVal</span> <span class="o">=</span> <span class="n">Step</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">StepVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// If not specified, use 1.0.</span>
+    <span class="n">StepVal</span> <span class="o">=</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">1.0</span><span class="p">));</span>
+  <span class="p">}</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">NextVar</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFAdd</span><span class="p">(</span><span class="n">Variable</span><span class="p">,</span> <span class="n">StepVal</span><span class="p">,</span> <span class="s">"nextvar"</span><span class="p">);</span>
+
+  <span class="c1">// Compute the end condition.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">EndCond</span> <span class="o">=</span> <span class="n">End</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">EndCond</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">EndCond</span><span class="p">;</span>
+
+  <span class="c1">// Convert condition to a bool by comparing equal to 0.0.</span>
+  <span class="n">EndCond</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpONE</span><span class="p">(</span>
+      <span class="n">EndCond</span><span class="p">,</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">)),</span> <span class="s">"loopcond"</span><span class="p">);</span>
+
+  <span class="c1">// Create the "after loop" block and insert it.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">LoopEndBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">AfterBB</span> <span class="o">=</span>
+      <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"afterloop"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+
+  <span class="c1">// Insert the conditional branch into the end of LoopEndBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCondBr</span><span class="p">(</span><span class="n">EndCond</span><span class="p">,</span> <span class="n">LoopBB</span><span class="p">,</span> <span class="n">AfterBB</span><span class="p">);</span>
+
+  <span class="c1">// Any new code will be inserted in AfterBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">AfterBB</span><span class="p">);</span>
+
+  <span class="c1">// Add a new entry to the PHI node for the backedge.</span>
+  <span class="n">Variable</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">NextVar</span><span class="p">,</span> <span class="n">LoopEndBB</span><span class="p">);</span>
+
+  <span class="c1">// Restore the unshadowed variable.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">OldVal</span><span class="p">)</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">OldVal</span><span class="p">;</span>
+  <span class="k">else</span>
+    <span class="n">NamedValues</span><span class="p">.</span><span class="n">erase</span><span class="p">(</span><span class="n">VarName</span><span class="p">);</span>
+
+  <span class="c1">// for expr always returns 0.0.</span>
+  <span class="k">return</span> <span class="n">Constant</span><span class="o">::</span><span class="n">getNullValue</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()));</span>
+<span class="p">}</span>
+
+<span class="n">Function</span> <span class="o">*</span><span class="n">PrototypeAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Make the function type:  double(double,double) etc.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">Type</span> <span class="o">*></span> <span class="n">Doubles</span><span class="p">(</span><span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">(),</span>
+                              <span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()));</span>
+  <span class="n">FunctionType</span> <span class="o">*</span><span class="n">FT</span> <span class="o">=</span>
+      <span class="n">FunctionType</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="n">Doubles</span><span class="p">,</span> <span class="nb">false</span><span class="p">);</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span>
+      <span class="n">Function</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">FT</span><span class="p">,</span> <span class="n">Function</span><span class="o">::</span><span class="n">ExternalLinkage</span><span class="p">,</span> <span class="n">Name</span><span class="p">,</span> <span class="n">TheModule</span><span class="p">);</span>
+
+  <span class="c1">// If F conflicted, there was already something named 'Name'.  If it has a</span>
+  <span class="c1">// body, don't allow redefinition or reextern.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">F</span><span class="o">-></span><span class="n">getName</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Name</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Delete the one we just made and get the existing one.</span>
+    <span class="n">F</span><span class="o">-></span><span class="n">eraseFromParent</span><span class="p">();</span>
+    <span class="n">F</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">Name</span><span class="p">);</span>
+
+    <span class="c1">// If F already has a body, reject this.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">F</span><span class="o">-></span><span class="n">empty</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">ErrorF</span><span class="p">(</span><span class="s">"redefinition of function"</span><span class="p">);</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+
+    <span class="c1">// If F took a different number of args, reject.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">F</span><span class="o">-></span><span class="n">arg_size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">ErrorF</span><span class="p">(</span><span class="s">"redefinition of function with different # args"</span><span class="p">);</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Set names for all arguments.</span>
+  <span class="kt">unsigned</span> <span class="n">Idx</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="n">Function</span><span class="o">::</span><span class="n">arg_iterator</span> <span class="n">AI</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">arg_begin</span><span class="p">();</span> <span class="n">Idx</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span>
+       <span class="o">++</span><span class="n">AI</span><span class="p">,</span> <span class="o">++</span><span class="n">Idx</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">AI</span><span class="o">-></span><span class="n">setName</span><span class="p">(</span><span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]);</span>
+
+    <span class="c1">// Add arguments to variable symbol table.</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]]</span> <span class="o">=</span> <span class="n">AI</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">return</span> <span class="n">F</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Function</span> <span class="o">*</span><span class="n">FunctionAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">NamedValues</span><span class="p">.</span><span class="n">clear</span><span class="p">();</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Proto</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">TheFunction</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Create a new basic block to start insertion into.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">BB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"entry"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">BB</span><span class="p">);</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">Value</span> <span class="o">*</span><span class="n">RetVal</span> <span class="o">=</span> <span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+    <span class="c1">// Finish off the function.</span>
+    <span class="n">Builder</span><span class="p">.</span><span class="n">CreateRet</span><span class="p">(</span><span class="n">RetVal</span><span class="p">);</span>
+
+    <span class="c1">// Validate the generated code, checking for consistency.</span>
+    <span class="n">verifyFunction</span><span class="p">(</span><span class="o">*</span><span class="n">TheFunction</span><span class="p">);</span>
+
+    <span class="c1">// Optimize the function.</span>
+    <span class="n">TheFPM</span><span class="o">-></span><span class="n">run</span><span class="p">(</span><span class="o">*</span><span class="n">TheFunction</span><span class="p">);</span>
+
+    <span class="k">return</span> <span class="n">TheFunction</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Error reading body, remove function.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">eraseFromParent</span><span class="p">();</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Top-Level parsing and JIT Driver</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="k">static</span> <span class="n">ExecutionEngine</span> <span class="o">*</span><span class="n">TheExecutionEngine</span><span class="p">;</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleDefinition</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">FunctionAST</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">ParseDefinition</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">LF</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Read function definition:"</span><span class="p">);</span>
+      <span class="n">LF</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleExtern</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">P</span> <span class="o">=</span> <span class="n">ParseExtern</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">P</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Read extern: "</span><span class="p">);</span>
+      <span class="n">F</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleTopLevelExpression</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Evaluate a top-level expression into an anonymous function.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">FunctionAST</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">ParseTopLevelExpr</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">LF</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">finalizeObject</span><span class="p">();</span>
+      <span class="c1">// JIT the function, returning a function pointer.</span>
+      <span class="kt">void</span> <span class="o">*</span><span class="n">FPtr</span> <span class="o">=</span> <span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">getPointerToFunction</span><span class="p">(</span><span class="n">LF</span><span class="p">);</span>
+
+      <span class="c1">// Cast it to the right type (takes no arguments, returns a double) so we</span>
+      <span class="c1">// can call it as a native function.</span>
+      <span class="kt">double</span> <span class="p">(</span><span class="o">*</span><span class="n">FP</span><span class="p">)()</span> <span class="o">=</span> <span class="p">(</span><span class="kt">double</span> <span class="p">(</span><span class="o">*</span><span class="p">)())(</span><span class="kt">intptr_t</span><span class="p">)</span><span class="n">FPtr</span><span class="p">;</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Evaluated to %f</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">FP</span><span class="p">());</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// top ::= definition | external | expression | ';'</span>
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">MainLoop</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"ready> "</span><span class="p">);</span>
+    <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">case</span> <span class="n">tok_eof</span>:
+      <span class="k">return</span><span class="p">;</span>
+    <span class="k">case</span> <span class="sc">';'</span>:
+      <span class="n">getNextToken</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span> <span class="c1">// ignore top-level semicolons.</span>
+    <span class="k">case</span> <span class="n">tok_def</span>:
+      <span class="n">HandleDefinition</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="k">case</span> <span class="n">tok_extern</span>:
+      <span class="n">HandleExtern</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="nl">default:</span>
+      <span class="n">HandleTopLevelExpression</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// "Library" functions that can be "extern'd" from user code.</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">/// putchard - putchar that takes a double and returns 0.</span>
+<span class="k">extern</span> <span class="s">"C"</span> <span class="kt">double</span> <span class="n">putchard</span><span class="p">(</span><span class="kt">double</span> <span class="n">X</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">putchar</span><span class="p">((</span><span class="kt">char</span><span class="p">)</span><span class="n">X</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Main driver code.</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="kt">int</span> <span class="n">main</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">InitializeNativeTarget</span><span class="p">();</span>
+  <span class="n">InitializeNativeTargetAsmPrinter</span><span class="p">();</span>
+  <span class="n">InitializeNativeTargetAsmParser</span><span class="p">();</span>
+  <span class="n">LLVMContext</span> <span class="o">&</span><span class="n">Context</span> <span class="o">=</span> <span class="n">getGlobalContext</span><span class="p">();</span>
+
+  <span class="c1">// Install standard binary operators.</span>
+  <span class="c1">// 1 is lowest precedence.</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'<'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'+'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'-'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'*'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">40</span><span class="p">;</span> <span class="c1">// highest.</span>
+
+  <span class="c1">// Prime the first token.</span>
+  <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"ready> "</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="c1">// Make the module, which holds all the code.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">unique_ptr</span><span class="o"><</span><span class="n">Module</span><span class="o">></span> <span class="n">Owner</span> <span class="o">=</span> <span class="n">make_unique</span><span class="o"><</span><span class="n">Module</span><span class="o">></span><span class="p">(</span><span class="s">"my cool jit"</span><span class="p">,</span> <span class="n">Context</span><span class="p">);</span>
+  <span class="n">TheModule</span> <span class="o">=</span> <span class="n">Owner</span><span class="p">.</span><span class="n">get</span><span class="p">();</span>
+
+  <span class="c1">// Create the JIT.  This takes ownership of the module.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">ErrStr</span><span class="p">;</span>
+  <span class="n">TheExecutionEngine</span> <span class="o">=</span>
+      <span class="n">EngineBuilder</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">move</span><span class="p">(</span><span class="n">Owner</span><span class="p">))</span>
+          <span class="p">.</span><span class="n">setErrorStr</span><span class="p">(</span><span class="o">&</span><span class="n">ErrStr</span><span class="p">)</span>
+          <span class="p">.</span><span class="n">setMCJITMemoryManager</span><span class="p">(</span><span class="n">llvm</span><span class="o">::</span><span class="n">make_unique</span><span class="o"><</span><span class="n">SectionMemoryManager</span><span class="o">></span><span class="p">())</span>
+          <span class="p">.</span><span class="n">create</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">TheExecutionEngine</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Could not create ExecutionEngine: %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">ErrStr</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+    <span class="n">exit</span><span class="p">(</span><span class="mi">1</span><span class="p">);</span>
+  <span class="p">}</span>
+
+  <span class="n">legacy</span><span class="o">::</span><span class="n">FunctionPassManager</span> <span class="n">OurFPM</span><span class="p">(</span><span class="n">TheModule</span><span class="p">);</span>
+
+  <span class="c1">// Set up the optimizer pipeline.  Start with registering info about how the</span>
+  <span class="c1">// target lays out data structures.</span>
+  <span class="n">TheModule</span><span class="o">-></span><span class="n">setDataLayout</span><span class="p">(</span><span class="o">*</span><span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">getDataLayout</span><span class="p">());</span>
+  <span class="c1">// Provide basic AliasAnalysis support for GVN.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createBasicAliasAnalysisPass</span><span class="p">());</span>
+  <span class="c1">// Do simple "peephole" optimizations and bit-twiddling optzns.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createInstructionCombiningPass</span><span class="p">());</span>
+  <span class="c1">// Reassociate expressions.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createReassociatePass</span><span class="p">());</span>
+  <span class="c1">// Eliminate Common SubExpressions.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createGVNPass</span><span class="p">());</span>
+  <span class="c1">// Simplify the control flow graph (deleting unreachable blocks, etc).</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createCFGSimplificationPass</span><span class="p">());</span>
+
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">doInitialization</span><span class="p">();</span>
+
+  <span class="c1">// Set the global so the code gen can use this.</span>
+  <span class="n">TheFPM</span> <span class="o">=</span> <span class="o">&</span><span class="n">OurFPM</span><span class="p">;</span>
+
+  <span class="c1">// Run the main "interpreter loop" now.</span>
+  <span class="n">MainLoop</span><span class="p">();</span>
+
+  <span class="n">TheFPM</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Print out all of the generated code.</span>
+  <span class="n">TheModule</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p><a class="reference external" href="LangImpl6.html">Next: Extending the language: user-defined operators</a></p>
+</div>
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+  <div class="section" id="kaleidoscope-extending-the-language-user-defined-operators">
+<h1>6. Kaleidoscope: Extending the Language: User-defined Operators<a class="headerlink" href="#kaleidoscope-extending-the-language-user-defined-operators" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#chapter-6-introduction" id="id1">Chapter 6 Introduction</a></li>
+<li><a class="reference internal" href="#user-defined-operators-the-idea" id="id2">User-defined Operators: the Idea</a></li>
+<li><a class="reference internal" href="#user-defined-binary-operators" id="id3">User-defined Binary Operators</a></li>
+<li><a class="reference internal" href="#user-defined-unary-operators" id="id4">User-defined Unary Operators</a></li>
+<li><a class="reference internal" href="#kicking-the-tires" id="id5">Kicking the Tires</a></li>
+<li><a class="reference internal" href="#full-code-listing" id="id6">Full Code Listing</a></li>
+</ul>
+</div>
+<div class="section" id="chapter-6-introduction">
+<h2><a class="toc-backref" href="#id1">6.1. Chapter 6 Introduction</a><a class="headerlink" href="#chapter-6-introduction" title="Permalink to this headline">¶</a></h2>
+<p>Welcome to Chapter 6 of the “<a class="reference external" href="index.html">Implementing a language with
+LLVM</a>” tutorial. At this point in our tutorial, we now
+have a fully functional language that is fairly minimal, but also
+useful. There is still one big problem with it, however. Our language
+doesn’t have many useful operators (like division, logical negation, or
+even any comparisons besides less-than).</p>
+<p>This chapter of the tutorial takes a wild digression into adding
+user-defined operators to the simple and beautiful Kaleidoscope
+language. This digression now gives us a simple and ugly language in
+some ways, but also a powerful one at the same time. One of the great
+things about creating your own language is that you get to decide what
+is good or bad. In this tutorial we’ll assume that it is okay to use
+this as a way to show some interesting parsing techniques.</p>
+<p>At the end of this tutorial, we’ll run through an example Kaleidoscope
+application that <a class="reference external" href="#example">renders the Mandelbrot set</a>. This gives an
+example of what you can build with Kaleidoscope and its feature set.</p>
+</div>
+<div class="section" id="user-defined-operators-the-idea">
+<h2><a class="toc-backref" href="#id2">6.2. User-defined Operators: the Idea</a><a class="headerlink" href="#user-defined-operators-the-idea" title="Permalink to this headline">¶</a></h2>
+<p>The “operator overloading” that we will add to Kaleidoscope is more
+general than languages like C++. In C++, you are only allowed to
+redefine existing operators: you can’t programatically change the
+grammar, introduce new operators, change precedence levels, etc. In this
+chapter, we will add this capability to Kaleidoscope, which will let the
+user round out the set of operators that are supported.</p>
+<p>The point of going into user-defined operators in a tutorial like this
+is to show the power and flexibility of using a hand-written parser.
+Thus far, the parser we have been implementing uses recursive descent
+for most parts of the grammar and operator precedence parsing for the
+expressions. See <a class="reference external" href="LangImpl2.html">Chapter 2</a> for details. Without
+using operator precedence parsing, it would be very difficult to allow
+the programmer to introduce new operators into the grammar: the grammar
+is dynamically extensible as the JIT runs.</p>
+<p>The two specific features we’ll add are programmable unary operators
+(right now, Kaleidoscope has no unary operators at all) as well as
+binary operators. An example of this is:</p>
+<div class="highlight-python"><div class="highlight"><pre># Logical unary not.
+def unary!(v)
+  if v then
+    0
+  else
+    1;
+
+# Define > with the same precedence as <.
+def binary> 10 (LHS RHS)
+  RHS < LHS;
+
+# Binary "logical or", (note that it does not "short circuit")
+def binary| 5 (LHS RHS)
+  if LHS then
+    1
+  else if RHS then
+    1
+  else
+    0;
+
+# Define = with slightly lower precedence than relationals.
+def binary= 9 (LHS RHS)
+  !(LHS < RHS | LHS > RHS);
+</pre></div>
+</div>
+<p>Many languages aspire to being able to implement their standard runtime
+library in the language itself. In Kaleidoscope, we can implement
+significant parts of the language in the library!</p>
+<p>We will break down implementation of these features into two parts:
+implementing support for user-defined binary operators and adding unary
+operators.</p>
+</div>
+<div class="section" id="user-defined-binary-operators">
+<h2><a class="toc-backref" href="#id3">6.3. User-defined Binary Operators</a><a class="headerlink" href="#user-defined-binary-operators" title="Permalink to this headline">¶</a></h2>
+<p>Adding support for user-defined binary operators is pretty simple with
+our current framework. We’ll first add support for the unary/binary
+keywords:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">enum</span> <span class="n">Token</span> <span class="p">{</span>
+  <span class="p">...</span>
+  <span class="c1">// operators</span>
+  <span class="n">tok_binary</span> <span class="o">=</span> <span class="o">-</span><span class="mi">11</span><span class="p">,</span> <span class="n">tok_unary</span> <span class="o">=</span> <span class="o">-</span><span class="mi">12</span>
+<span class="p">};</span>
+<span class="p">...</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="n">gettok</span><span class="p">()</span> <span class="p">{</span>
+<span class="p">...</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"for"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_for</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"in"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_in</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"binary"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_binary</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"unary"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_unary</span><span class="p">;</span>
+    <span class="k">return</span> <span class="n">tok_identifier</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>This just adds lexer support for the unary and binary keywords, like we
+did in <a class="reference external" href="LangImpl5.html#iflexer">previous chapters</a>. One nice thing
+about our current AST, is that we represent binary operators with full
+generalisation by using their ASCII code as the opcode. For our extended
+operators, we’ll use this same representation, so we don’t need any new
+AST or parser support.</p>
+<p>On the other hand, we have to be able to represent the definitions of
+these new operators, in the “def binary| 5” part of the function
+definition. In our grammar so far, the “name” for the function
+definition is parsed as the “prototype” production and into the
+<tt class="docutils literal"><span class="pre">PrototypeAST</span></tt> AST node. To represent our new user-defined operators
+as prototypes, we have to extend the <tt class="docutils literal"><span class="pre">PrototypeAST</span></tt> AST node like
+this:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// PrototypeAST - This class represents the "prototype" for a function,</span>
+<span class="c1">/// which captures its argument names as well as if it is an operator.</span>
+<span class="k">class</span> <span class="nc">PrototypeAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">Args</span><span class="p">;</span>
+  <span class="kt">bool</span> <span class="n">isOperator</span><span class="p">;</span>
+  <span class="kt">unsigned</span> <span class="n">Precedence</span><span class="p">;</span>  <span class="c1">// Precedence if a binary op.</span>
+<span class="nl">public:</span>
+  <span class="n">PrototypeAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">name</span><span class="p">,</span> <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="o">&</span><span class="n">args</span><span class="p">,</span>
+               <span class="kt">bool</span> <span class="n">isoperator</span> <span class="o">=</span> <span class="nb">false</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">prec</span> <span class="o">=</span> <span class="mi">0</span><span class="p">)</span>
+  <span class="o">:</span> <span class="n">Name</span><span class="p">(</span><span class="n">name</span><span class="p">),</span> <span class="n">Args</span><span class="p">(</span><span class="n">args</span><span class="p">),</span> <span class="n">isOperator</span><span class="p">(</span><span class="n">isoperator</span><span class="p">),</span> <span class="n">Precedence</span><span class="p">(</span><span class="n">prec</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="kt">bool</span> <span class="n">isUnaryOp</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">isOperator</span> <span class="o">&&</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">==</span> <span class="mi">1</span><span class="p">;</span> <span class="p">}</span>
+  <span class="kt">bool</span> <span class="n">isBinaryOp</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">isOperator</span> <span class="o">&&</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">==</span> <span class="mi">2</span><span class="p">;</span> <span class="p">}</span>
+
+  <span class="kt">char</span> <span class="n">getOperatorName</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span>
+    <span class="n">assert</span><span class="p">(</span><span class="n">isUnaryOp</span><span class="p">()</span> <span class="o">||</span> <span class="n">isBinaryOp</span><span class="p">());</span>
+    <span class="k">return</span> <span class="n">Name</span><span class="p">[</span><span class="n">Name</span><span class="p">.</span><span class="n">size</span><span class="p">()</span><span class="o">-</span><span class="mi">1</span><span class="p">];</span>
+  <span class="p">}</span>
+
+  <span class="kt">unsigned</span> <span class="n">getBinaryPrecedence</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">Precedence</span><span class="p">;</span> <span class="p">}</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>Basically, in addition to knowing a name for the prototype, we now keep
+track of whether it was an operator, and if it was, what precedence
+level the operator is at. The precedence is only used for binary
+operators (as you’ll see below, it just doesn’t apply for unary
+operators). Now that we have a way to represent the prototype for a
+user-defined operator, we need to parse it:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// prototype</span>
+<span class="c1">///   ::= id '(' id* ')'</span>
+<span class="c1">///   ::= binary LETTER number? (id, id)</span>
+<span class="k">static</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ParsePrototype</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">FnName</span><span class="p">;</span>
+
+  <span class="kt">unsigned</span> <span class="n">Kind</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>  <span class="c1">// 0 = identifier, 1 = unary, 2 = binary.</span>
+  <span class="kt">unsigned</span> <span class="n">BinaryPrecedence</span> <span class="o">=</span> <span class="mi">30</span><span class="p">;</span>
+
+  <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="nl">default:</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected function name in prototype"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>:
+    <span class="n">FnName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_binary</span>:
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+      <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected binary operator"</span><span class="p">);</span>
+    <span class="n">FnName</span> <span class="o">=</span> <span class="s">"binary"</span><span class="p">;</span>
+    <span class="n">FnName</span> <span class="o">+=</span> <span class="p">(</span><span class="kt">char</span><span class="p">)</span><span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+
+    <span class="c1">// Read the precedence if present.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="n">tok_number</span><span class="p">)</span> <span class="p">{</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">NumVal</span> <span class="o"><</span> <span class="mi">1</span> <span class="o">||</span> <span class="n">NumVal</span> <span class="o">></span> <span class="mi">100</span><span class="p">)</span>
+        <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Invalid precedecnce: must be 1..100"</span><span class="p">);</span>
+      <span class="n">BinaryPrecedence</span> <span class="o">=</span> <span class="p">(</span><span class="kt">unsigned</span><span class="p">)</span><span class="n">NumVal</span><span class="p">;</span>
+      <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="p">}</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'('</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected '(' in prototype"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">ArgNames</span><span class="p">;</span>
+  <span class="k">while</span> <span class="p">(</span><span class="n">getNextToken</span><span class="p">()</span> <span class="o">==</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="n">ArgNames</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">IdentifierStr</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected ')' in prototype"</span><span class="p">);</span>
+
+  <span class="c1">// success.</span>
+  <span class="n">getNextToken</span><span class="p">();</span>  <span class="c1">// eat ')'.</span>
+
+  <span class="c1">// Verify right number of names for operator.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Kind</span> <span class="o">&&</span> <span class="n">ArgNames</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Kind</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Invalid number of operands for operator"</span><span class="p">);</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">PrototypeAST</span><span class="p">(</span><span class="n">FnName</span><span class="p">,</span> <span class="n">ArgNames</span><span class="p">,</span> <span class="n">Kind</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">BinaryPrecedence</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>This is all fairly straightforward parsing code, and we have already
+seen a lot of similar code in the past. One interesting part about the
+code above is the couple lines that set up <tt class="docutils literal"><span class="pre">FnName</span></tt> for binary
+operators. This builds names like “binary@” for a newly defined “@”
+operator. This then takes advantage of the fact that symbol names in the
+LLVM symbol table are allowed to have any character in them, including
+embedded nul characters.</p>
+<p>The next interesting thing to add, is codegen support for these binary
+operators. Given our current structure, this is a simple addition of a
+default case for our existing binary operator node:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">Value</span> <span class="o">*</span><span class="n">BinaryExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">L</span> <span class="o">=</span> <span class="n">LHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">R</span> <span class="o">=</span> <span class="n">RHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">L</span> <span class="o">==</span> <span class="mi">0</span> <span class="o">||</span> <span class="n">R</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">switch</span> <span class="p">(</span><span class="n">Op</span><span class="p">)</span> <span class="p">{</span>
+  <span class="k">case</span> <span class="sc">'+'</span>: <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFAdd</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"addtmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'-'</span>: <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFSub</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"subtmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'*'</span>: <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFMul</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"multmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'<'</span>:
+    <span class="n">L</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpULT</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"cmptmp"</span><span class="p">);</span>
+    <span class="c1">// Convert bool 0/1 to double 0.0 or 1.0</span>
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateUIToFP</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span>
+                                <span class="s">"booltmp"</span><span class="p">);</span>
+  <span class="nl">default:</span> <span class="k">break</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="c1">// If it wasn't a builtin binary operator, it must be a user defined one. Emit</span>
+  <span class="c1">// a call to it.</span>
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">(</span><span class="s">"binary"</span><span class="p">)</span><span class="o">+</span><span class="n">Op</span><span class="p">);</span>
+  <span class="n">assert</span><span class="p">(</span><span class="n">F</span> <span class="o">&&</span> <span class="s">"binary operator not found!"</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Ops</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span> <span class="o">=</span> <span class="p">{</span> <span class="n">L</span><span class="p">,</span> <span class="n">R</span> <span class="p">};</span>
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">F</span><span class="p">,</span> <span class="n">Ops</span><span class="p">,</span> <span class="s">"binop"</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>As you can see above, the new code is actually really simple. It just
+does a lookup for the appropriate operator in the symbol table and
+generates a function call to it. Since user-defined operators are just
+built as normal functions (because the “prototype” boils down to a
+function with the right name) everything falls into place.</p>
+<p>The final piece of code we are missing, is a bit of top-level magic:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">Function</span> <span class="o">*</span><span class="n">FunctionAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">NamedValues</span><span class="p">.</span><span class="n">clear</span><span class="p">();</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Proto</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">TheFunction</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// If this is an operator, install it.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Proto</span><span class="o">-></span><span class="n">isBinaryOp</span><span class="p">())</span>
+    <span class="n">BinopPrecedence</span><span class="p">[</span><span class="n">Proto</span><span class="o">-></span><span class="n">getOperatorName</span><span class="p">()]</span> <span class="o">=</span> <span class="n">Proto</span><span class="o">-></span><span class="n">getBinaryPrecedence</span><span class="p">();</span>
+
+  <span class="c1">// Create a new basic block to start insertion into.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">BB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"entry"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">BB</span><span class="p">);</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">Value</span> <span class="o">*</span><span class="n">RetVal</span> <span class="o">=</span> <span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+    <span class="p">...</span>
+</pre></div>
+</div>
+<p>Basically, before codegening a function, if it is a user-defined
+operator, we register it in the precedence table. This allows the binary
+operator parsing logic we already have in place to handle it. Since we
+are working on a fully-general operator precedence parser, this is all
+we need to do to “extend the grammar”.</p>
+<p>Now we have useful user-defined binary operators. This builds a lot on
+the previous framework we built for other operators. Adding unary
+operators is a bit more challenging, because we don’t have any framework
+for it yet - lets see what it takes.</p>
+</div>
+<div class="section" id="user-defined-unary-operators">
+<h2><a class="toc-backref" href="#id4">6.4. User-defined Unary Operators</a><a class="headerlink" href="#user-defined-unary-operators" title="Permalink to this headline">¶</a></h2>
+<p>Since we don’t currently support unary operators in the Kaleidoscope
+language, we’ll need to add everything to support them. Above, we added
+simple support for the ‘unary’ keyword to the lexer. In addition to
+that, we need an AST node:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// UnaryExprAST - Expression class for a unary operator.</span>
+<span class="k">class</span> <span class="nc">UnaryExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">char</span> <span class="n">Opcode</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Operand</span><span class="p">;</span>
+<span class="nl">public:</span>
+  <span class="n">UnaryExprAST</span><span class="p">(</span><span class="kt">char</span> <span class="n">opcode</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">operand</span><span class="p">)</span>
+    <span class="o">:</span> <span class="n">Opcode</span><span class="p">(</span><span class="n">opcode</span><span class="p">),</span> <span class="n">Operand</span><span class="p">(</span><span class="n">operand</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="k">virtual</span> <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>This AST node is very simple and obvious by now. It directly mirrors the
+binary operator AST node, except that it only has one child. With this,
+we need to add the parsing logic. Parsing a unary operator is pretty
+simple: we’ll add a new function to do it:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// unary</span>
+<span class="c1">///   ::= primary</span>
+<span class="c1">///   ::= '!' unary</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseUnary</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// If the current token is not an operator, it must be a primary expr.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="o">||</span> <span class="n">CurTok</span> <span class="o">==</span> <span class="sc">'('</span> <span class="o">||</span> <span class="n">CurTok</span> <span class="o">==</span> <span class="sc">','</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ParsePrimary</span><span class="p">();</span>
+
+  <span class="c1">// If this is a unary operator, read it.</span>
+  <span class="kt">int</span> <span class="n">Opc</span> <span class="o">=</span> <span class="n">CurTok</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">Operand</span> <span class="o">=</span> <span class="n">ParseUnary</span><span class="p">())</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">UnaryExprAST</span><span class="p">(</span><span class="n">Opc</span><span class="p">,</span> <span class="n">Operand</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>The grammar we add is pretty straightforward here. If we see a unary
+operator when parsing a primary operator, we eat the operator as a
+prefix and parse the remaining piece as another unary operator. This
+allows us to handle multiple unary operators (e.g. ”!!x”). Note that
+unary operators can’t have ambiguous parses like binary operators can,
+so there is no need for precedence information.</p>
+<p>The problem with this function, is that we need to call ParseUnary from
+somewhere. To do this, we change previous callers of ParsePrimary to
+call ParseUnary instead:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// binoprhs</span>
+<span class="c1">///   ::= ('+' unary)*</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseBinOpRHS</span><span class="p">(</span><span class="kt">int</span> <span class="n">ExprPrec</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span><span class="p">)</span> <span class="p">{</span>
+  <span class="p">...</span>
+    <span class="c1">// Parse the unary expression after the binary operator.</span>
+    <span class="n">ExprAST</span> <span class="o">*</span><span class="n">RHS</span> <span class="o">=</span> <span class="n">ParseUnary</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">RHS</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">...</span>
+<span class="p">}</span>
+<span class="c1">/// expression</span>
+<span class="c1">///   ::= unary binoprhs</span>
+<span class="c1">///</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseExpression</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span> <span class="o">=</span> <span class="n">ParseUnary</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">LHS</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="n">ParseBinOpRHS</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">LHS</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>With these two simple changes, we are now able to parse unary operators
+and build the AST for them. Next up, we need to add parser support for
+prototypes, to parse the unary operator prototype. We extend the binary
+operator code above with:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// prototype</span>
+<span class="c1">///   ::= id '(' id* ')'</span>
+<span class="c1">///   ::= binary LETTER number? (id, id)</span>
+<span class="c1">///   ::= unary LETTER (id)</span>
+<span class="k">static</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ParsePrototype</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">FnName</span><span class="p">;</span>
+
+  <span class="kt">unsigned</span> <span class="n">Kind</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>  <span class="c1">// 0 = identifier, 1 = unary, 2 = binary.</span>
+  <span class="kt">unsigned</span> <span class="n">BinaryPrecedence</span> <span class="o">=</span> <span class="mi">30</span><span class="p">;</span>
+
+  <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="nl">default:</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected function name in prototype"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>:
+    <span class="n">FnName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_unary</span>:
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+      <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected unary operator"</span><span class="p">);</span>
+    <span class="n">FnName</span> <span class="o">=</span> <span class="s">"unary"</span><span class="p">;</span>
+    <span class="n">FnName</span> <span class="o">+=</span> <span class="p">(</span><span class="kt">char</span><span class="p">)</span><span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_binary</span>:
+    <span class="p">...</span>
+</pre></div>
+</div>
+<p>As with binary operators, we name unary operators with a name that
+includes the operator character. This assists us at code generation
+time. Speaking of, the final piece we need to add is codegen support for
+unary operators. It looks like this:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">Value</span> <span class="o">*</span><span class="n">UnaryExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">OperandV</span> <span class="o">=</span> <span class="n">Operand</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">OperandV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">(</span><span class="s">"unary"</span><span class="p">)</span><span class="o">+</span><span class="n">Opcode</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">F</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown unary operator"</span><span class="p">);</span>
+
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">F</span><span class="p">,</span> <span class="n">OperandV</span><span class="p">,</span> <span class="s">"unop"</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>This code is similar to, but simpler than, the code for binary
+operators. It is simpler primarily because it doesn’t need to handle any
+predefined operators.</p>
+</div>
+<div class="section" id="kicking-the-tires">
+<h2><a class="toc-backref" href="#id5">6.5. Kicking the Tires</a><a class="headerlink" href="#kicking-the-tires" title="Permalink to this headline">¶</a></h2>
+<p>It is somewhat hard to believe, but with a few simple extensions we’ve
+covered in the last chapters, we have grown a real-ish language. With
+this, we can do a lot of interesting things, including I/O, math, and a
+bunch of other things. For example, we can now add a nice sequencing
+operator (printd is defined to print out the specified value and a
+newline):</p>
+<div class="highlight-python"><div class="highlight"><pre>ready> extern printd(x);
+Read extern:
+declare double @printd(double)
+
+ready> def binary : 1 (x y) 0;  # Low-precedence operator that ignores operands.
+..
+ready> printd(123) : printd(456) : printd(789);
+123.000000
+456.000000
+789.000000
+Evaluated to 0.000000
+</pre></div>
+</div>
+<p>We can also define a bunch of other “primitive” operations, such as:</p>
+<div class="highlight-python"><div class="highlight"><pre># Logical unary not.
+def unary!(v)
+  if v then
+    0
+  else
+    1;
+
+# Unary negate.
+def unary-(v)
+  0-v;
+
+# Define > with the same precedence as <.
+def binary> 10 (LHS RHS)
+  RHS < LHS;
+
+# Binary logical or, which does not short circuit.
+def binary| 5 (LHS RHS)
+  if LHS then
+    1
+  else if RHS then
+    1
+  else
+    0;
+
+# Binary logical and, which does not short circuit.
+def binary& 6 (LHS RHS)
+  if !LHS then
+    0
+  else
+    !!RHS;
+
+# Define = with slightly lower precedence than relationals.
+def binary = 9 (LHS RHS)
+  !(LHS < RHS | LHS > RHS);
+
+# Define ':' for sequencing: as a low-precedence operator that ignores operands
+# and just returns the RHS.
+def binary : 1 (x y) y;
+</pre></div>
+</div>
+<p>Given the previous if/then/else support, we can also define interesting
+functions for I/O. For example, the following prints out a character
+whose “density” reflects the value passed in: the lower the value, the
+denser the character:</p>
+<div class="highlight-python"><div class="highlight"><pre>ready>
+
+extern putchard(char)
+def printdensity(d)
+  if d > 8 then
+    putchard(32)  # ' '
+  else if d > 4 then
+    putchard(46)  # '.'
+  else if d > 2 then
+    putchard(43)  # '+'
+  else
+    putchard(42); # '*'
+...
+ready> printdensity(1): printdensity(2): printdensity(3):
+       printdensity(4): printdensity(5): printdensity(9):
+       putchard(10);
+**++.
+Evaluated to 0.000000
+</pre></div>
+</div>
+<p>Based on these simple primitive operations, we can start to define more
+interesting things. For example, here’s a little function that solves
+for the number of iterations it takes a function in the complex plane to
+converge:</p>
+<div class="highlight-python"><div class="highlight"><pre># Determine whether the specific location diverges.
+# Solve for z = z^2 + c in the complex plane.
+def mandleconverger(real imag iters creal cimag)
+  if iters > 255 | (real*real + imag*imag > 4) then
+    iters
+  else
+    mandleconverger(real*real - imag*imag + creal,
+                    2*real*imag + cimag,
+                    iters+1, creal, cimag);
+
+# Return the number of iterations required for the iteration to escape
+def mandleconverge(real imag)
+  mandleconverger(real, imag, 0, real, imag);
+</pre></div>
+</div>
+<p>This “<tt class="docutils literal"><span class="pre">z</span> <span class="pre">=</span> <span class="pre">z2</span> <span class="pre">+</span> <span class="pre">c</span></tt>” function is a beautiful little creature that is
+the basis for computation of the <a class="reference external" href="http://en.wikipedia.org/wiki/Mandelbrot_set">Mandelbrot
+Set</a>. Our
+<tt class="docutils literal"><span class="pre">mandelconverge</span></tt> function returns the number of iterations that it
+takes for a complex orbit to escape, saturating to 255. This is not a
+very useful function by itself, but if you plot its value over a
+two-dimensional plane, you can see the Mandelbrot set. Given that we are
+limited to using putchard here, our amazing graphical output is limited,
+but we can whip together something using the density plotter above:</p>
+<div class="highlight-python"><div class="highlight"><pre># Compute and plot the mandlebrot set with the specified 2 dimensional range
+# info.
+def mandelhelp(xmin xmax xstep   ymin ymax ystep)
+  for y = ymin, y < ymax, ystep in (
+    (for x = xmin, x < xmax, xstep in
+       printdensity(mandleconverge(x,y)))
+    : putchard(10)
+  )
+
+# mandel - This is a convenient helper function for plotting the mandelbrot set
+# from the specified position with the specified Magnification.
+def mandel(realstart imagstart realmag imagmag)
+  mandelhelp(realstart, realstart+realmag*78, realmag,
+             imagstart, imagstart+imagmag*40, imagmag);
+</pre></div>
+</div>
+<p>Given this, we can try plotting out the mandlebrot set! Lets try it out:</p>
+<div class="highlight-python"><div class="highlight"><pre>ready> mandel(-2.3, -1.3, 0.05, 0.07);
+*******************************+++++++++++*************************************
+*************************+++++++++++++++++++++++*******************************
+**********************+++++++++++++++++++++++++++++****************************
+*******************+++++++++++++++++++++.. ...++++++++*************************
+*****************++++++++++++++++++++++.... ...+++++++++***********************
+***************+++++++++++++++++++++++.....   ...+++++++++*********************
+**************+++++++++++++++++++++++....     ....+++++++++********************
+*************++++++++++++++++++++++......      .....++++++++*******************
+************+++++++++++++++++++++.......       .......+++++++******************
+***********+++++++++++++++++++....                ... .+++++++*****************
+**********+++++++++++++++++.......                     .+++++++****************
+*********++++++++++++++...........                    ...+++++++***************
+********++++++++++++............                      ...++++++++**************
+********++++++++++... ..........                        .++++++++**************
+*******+++++++++.....                                   .+++++++++*************
+*******++++++++......                                  ..+++++++++*************
+*******++++++.......                                   ..+++++++++*************
+*******+++++......                                     ..+++++++++*************
+*******.... ....                                      ...+++++++++*************
+*******.... .                                         ...+++++++++*************
+*******+++++......                                    ...+++++++++*************
+*******++++++.......                                   ..+++++++++*************
+*******++++++++......                                   .+++++++++*************
+*******+++++++++.....                                  ..+++++++++*************
+********++++++++++... ..........                        .++++++++**************
+********++++++++++++............                      ...++++++++**************
+*********++++++++++++++..........                     ...+++++++***************
+**********++++++++++++++++........                     .+++++++****************
+**********++++++++++++++++++++....                ... ..+++++++****************
+***********++++++++++++++++++++++.......       .......++++++++*****************
+************+++++++++++++++++++++++......      ......++++++++******************
+**************+++++++++++++++++++++++....      ....++++++++********************
+***************+++++++++++++++++++++++.....   ...+++++++++*********************
+*****************++++++++++++++++++++++....  ...++++++++***********************
+*******************+++++++++++++++++++++......++++++++*************************
+*********************++++++++++++++++++++++.++++++++***************************
+*************************+++++++++++++++++++++++*******************************
+******************************+++++++++++++************************************
+*******************************************************************************
+*******************************************************************************
+*******************************************************************************
+Evaluated to 0.000000
+ready> mandel(-2, -1, 0.02, 0.04);
+**************************+++++++++++++++++++++++++++++++++++++++++++++++++++++
+***********************++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+*********************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.
+*******************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++...
+*****************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.....
+***************++++++++++++++++++++++++++++++++++++++++++++++++++++++++........
+**************++++++++++++++++++++++++++++++++++++++++++++++++++++++...........
+************+++++++++++++++++++++++++++++++++++++++++++++++++++++..............
+***********++++++++++++++++++++++++++++++++++++++++++++++++++........        .
+**********++++++++++++++++++++++++++++++++++++++++++++++.............
+********+++++++++++++++++++++++++++++++++++++++++++..................
+*******+++++++++++++++++++++++++++++++++++++++.......................
+******+++++++++++++++++++++++++++++++++++...........................
+*****++++++++++++++++++++++++++++++++............................
+*****++++++++++++++++++++++++++++...............................
+****++++++++++++++++++++++++++......   .........................
+***++++++++++++++++++++++++.........     ......    ...........
+***++++++++++++++++++++++............
+**+++++++++++++++++++++..............
+**+++++++++++++++++++................
+*++++++++++++++++++.................
+*++++++++++++++++............ ...
+*++++++++++++++..............
+*+++....++++................
+*..........  ...........
+*
+*..........  ...........
+*+++....++++................
+*++++++++++++++..............
+*++++++++++++++++............ ...
+*++++++++++++++++++.................
+**+++++++++++++++++++................
+**+++++++++++++++++++++..............
+***++++++++++++++++++++++............
+***++++++++++++++++++++++++.........     ......    ...........
+****++++++++++++++++++++++++++......   .........................
+*****++++++++++++++++++++++++++++...............................
+*****++++++++++++++++++++++++++++++++............................
+******+++++++++++++++++++++++++++++++++++...........................
+*******+++++++++++++++++++++++++++++++++++++++.......................
+********+++++++++++++++++++++++++++++++++++++++++++..................
+Evaluated to 0.000000
+ready> mandel(-0.9, -1.4, 0.02, 0.03);
+*******************************************************************************
+*******************************************************************************
+*******************************************************************************
+**********+++++++++++++++++++++************************************************
+*+++++++++++++++++++++++++++++++++++++++***************************************
++++++++++++++++++++++++++++++++++++++++++++++**********************************
+++++++++++++++++++++++++++++++++++++++++++++++++++*****************************
+++++++++++++++++++++++++++++++++++++++++++++++++++++++*************************
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++**********************
++++++++++++++++++++++++++++++++++.........++++++++++++++++++*******************
++++++++++++++++++++++++++++++++....   ......+++++++++++++++++++****************
++++++++++++++++++++++++++++++.......  ........+++++++++++++++++++**************
+++++++++++++++++++++++++++++........   ........++++++++++++++++++++************
++++++++++++++++++++++++++++.........     ..  ...+++++++++++++++++++++**********
+++++++++++++++++++++++++++...........        ....++++++++++++++++++++++********
+++++++++++++++++++++++++.............       .......++++++++++++++++++++++******
++++++++++++++++++++++++.............        ........+++++++++++++++++++++++****
+++++++++++++++++++++++...........           ..........++++++++++++++++++++++***
+++++++++++++++++++++...........                .........++++++++++++++++++++++*
+++++++++++++++++++............                  ...........++++++++++++++++++++
+++++++++++++++++...............                 .............++++++++++++++++++
+++++++++++++++.................                 ...............++++++++++++++++
+++++++++++++..................                  .................++++++++++++++
++++++++++..................                      .................+++++++++++++
+++++++........        .                               .........  ..++++++++++++
+++............                                         ......    ....++++++++++
+..............                                                    ...++++++++++
+..............                                                    ....+++++++++
+..............                                                    .....++++++++
+.............                                                    ......++++++++
+...........                                                     .......++++++++
+.........                                                       ........+++++++
+.........                                                       ........+++++++
+.........                                                           ....+++++++
+........                                                             ...+++++++
+.......                                                              ...+++++++
+                                                                    ....+++++++
+                                                                   .....+++++++
+                                                                    ....+++++++
+                                                                    ....+++++++
+                                                                    ....+++++++
+Evaluated to 0.000000
+ready> ^D
+</pre></div>
+</div>
+<p>At this point, you may be starting to realize that Kaleidoscope is a
+real and powerful language. It may not be self-similar :), but it can be
+used to plot things that are!</p>
+<p>With this, we conclude the “adding user-defined operators” chapter of
+the tutorial. We have successfully augmented our language, adding the
+ability to extend the language in the library, and we have shown how
+this can be used to build a simple but interesting end-user application
+in Kaleidoscope. At this point, Kaleidoscope can build a variety of
+applications that are functional and can call functions with
+side-effects, but it can’t actually define and mutate a variable itself.</p>
+<p>Strikingly, variable mutation is an important feature of some languages,
+and it is not at all obvious how to <a class="reference external" href="LangImpl7.html">add support for mutable
+variables</a> without having to add an “SSA construction”
+phase to your front-end. In the next chapter, we will describe how you
+can add variable mutation without building SSA in your front-end.</p>
+</div>
+<div class="section" id="full-code-listing">
+<h2><a class="toc-backref" href="#id6">6.6. Full Code Listing</a><a class="headerlink" href="#full-code-listing" title="Permalink to this headline">¶</a></h2>
+<p>Here is the complete code listing for our running example, enhanced with
+the if/then/else and for expressions.. To build this example, use:</p>
+<div class="highlight-bash"><div class="highlight"><pre><span class="c"># Compile</span>
+clang++ -g toy.cpp <span class="sb">`</span>llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native<span class="sb">`</span> -O3 -o toy
+<span class="c"># Run</span>
+./toy
+</pre></div>
+</div>
+<p>On some platforms, you will need to specify -rdynamic or
+-Wl,–export-dynamic when linking. This ensures that symbols defined in
+the main executable are exported to the dynamic linker and so are
+available for symbol resolution at run time. This is not needed if you
+compile your support code into a shared library, although doing that
+will cause problems on Windows.</p>
+<p>Here is the code:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include "llvm/ADT/STLExtras.h"</span>
+<span class="cp">#include "llvm/Analysis/Passes.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/ExecutionEngine.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/MCJIT.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/SectionMemoryManager.h"</span>
+<span class="cp">#include "llvm/IR/DataLayout.h"</span>
+<span class="cp">#include "llvm/IR/DerivedTypes.h"</span>
+<span class="cp">#include "llvm/IR/IRBuilder.h"</span>
+<span class="cp">#include "llvm/IR/LLVMContext.h"</span>
+<span class="cp">#include "llvm/IR/LegacyPassManager.h"</span>
+<span class="cp">#include "llvm/IR/Module.h"</span>
+<span class="cp">#include "llvm/IR/Verifier.h"</span>
+<span class="cp">#include "llvm/Support/TargetSelect.h"</span>
+<span class="cp">#include "llvm/Transforms/Scalar.h"</span>
+<span class="cp">#include <cctype></span>
+<span class="cp">#include <cstdio></span>
+<span class="cp">#include <map></span>
+<span class="cp">#include <string></span>
+<span class="cp">#include <vector></span>
+<span class="k">using</span> <span class="k">namespace</span> <span class="n">llvm</span><span class="p">;</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Lexer</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">// The lexer returns tokens [0-255] if it is an unknown character, otherwise one</span>
+<span class="c1">// of these for known things.</span>
+<span class="k">enum</span> <span class="n">Token</span> <span class="p">{</span>
+  <span class="n">tok_eof</span> <span class="o">=</span> <span class="o">-</span><span class="mi">1</span><span class="p">,</span>
+
+  <span class="c1">// commands</span>
+  <span class="n">tok_def</span> <span class="o">=</span> <span class="o">-</span><span class="mi">2</span><span class="p">,</span>
+  <span class="n">tok_extern</span> <span class="o">=</span> <span class="o">-</span><span class="mi">3</span><span class="p">,</span>
+
+  <span class="c1">// primary</span>
+  <span class="n">tok_identifier</span> <span class="o">=</span> <span class="o">-</span><span class="mi">4</span><span class="p">,</span>
+  <span class="n">tok_number</span> <span class="o">=</span> <span class="o">-</span><span class="mi">5</span><span class="p">,</span>
+
+  <span class="c1">// control</span>
+  <span class="n">tok_if</span> <span class="o">=</span> <span class="o">-</span><span class="mi">6</span><span class="p">,</span>
+  <span class="n">tok_then</span> <span class="o">=</span> <span class="o">-</span><span class="mi">7</span><span class="p">,</span>
+  <span class="n">tok_else</span> <span class="o">=</span> <span class="o">-</span><span class="mi">8</span><span class="p">,</span>
+  <span class="n">tok_for</span> <span class="o">=</span> <span class="o">-</span><span class="mi">9</span><span class="p">,</span>
+  <span class="n">tok_in</span> <span class="o">=</span> <span class="o">-</span><span class="mi">10</span><span class="p">,</span>
+
+  <span class="c1">// operators</span>
+  <span class="n">tok_binary</span> <span class="o">=</span> <span class="o">-</span><span class="mi">11</span><span class="p">,</span>
+  <span class="n">tok_unary</span> <span class="o">=</span> <span class="o">-</span><span class="mi">12</span>
+<span class="p">};</span>
+
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdentifierStr</span><span class="p">;</span> <span class="c1">// Filled in if tok_identifier</span>
+<span class="k">static</span> <span class="kt">double</span> <span class="n">NumVal</span><span class="p">;</span>             <span class="c1">// Filled in if tok_number</span>
+
+<span class="c1">/// gettok - Return the next token from standard input.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">gettok</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">static</span> <span class="kt">int</span> <span class="n">LastChar</span> <span class="o">=</span> <span class="sc">' '</span><span class="p">;</span>
+
+  <span class="c1">// Skip any whitespace.</span>
+  <span class="k">while</span> <span class="p">(</span><span class="n">isspace</span><span class="p">(</span><span class="n">LastChar</span><span class="p">))</span>
+    <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">isalpha</span><span class="p">(</span><span class="n">LastChar</span><span class="p">))</span> <span class="p">{</span> <span class="c1">// identifier: [a-zA-Z][a-zA-Z0-9]*</span>
+    <span class="n">IdentifierStr</span> <span class="o">=</span> <span class="n">LastChar</span><span class="p">;</span>
+    <span class="k">while</span> <span class="p">(</span><span class="n">isalnum</span><span class="p">((</span><span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">())))</span>
+      <span class="n">IdentifierStr</span> <span class="o">+=</span> <span class="n">LastChar</span><span class="p">;</span>
+
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"def"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_def</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"extern"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_extern</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"if"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_if</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"then"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_then</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"else"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_else</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"for"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_for</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"in"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_in</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"binary"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_binary</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"unary"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_unary</span><span class="p">;</span>
+    <span class="k">return</span> <span class="n">tok_identifier</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">isdigit</span><span class="p">(</span><span class="n">LastChar</span><span class="p">)</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">)</span> <span class="p">{</span> <span class="c1">// Number: [0-9.]+</span>
+    <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">NumStr</span><span class="p">;</span>
+    <span class="k">do</span> <span class="p">{</span>
+      <span class="n">NumStr</span> <span class="o">+=</span> <span class="n">LastChar</span><span class="p">;</span>
+      <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+    <span class="p">}</span> <span class="k">while</span> <span class="p">(</span><span class="n">isdigit</span><span class="p">(</span><span class="n">LastChar</span><span class="p">)</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">);</span>
+
+    <span class="n">NumVal</span> <span class="o">=</span> <span class="n">strtod</span><span class="p">(</span><span class="n">NumStr</span><span class="p">.</span><span class="n">c_str</span><span class="p">(),</span> <span class="mi">0</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">tok_number</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'#'</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Comment until end of line.</span>
+    <span class="k">do</span>
+      <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+    <span class="k">while</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">!=</span> <span class="n">EOF</span> <span class="o">&&</span> <span class="n">LastChar</span> <span class="o">!=</span> <span class="sc">'\n'</span> <span class="o">&&</span> <span class="n">LastChar</span> <span class="o">!=</span> <span class="sc">'\r'</span><span class="p">);</span>
+
+    <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">!=</span> <span class="n">EOF</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">gettok</span><span class="p">();</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Check for end of file.  Don't eat the EOF.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="n">EOF</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">tok_eof</span><span class="p">;</span>
+
+  <span class="c1">// Otherwise, just return the character as its ascii value.</span>
+  <span class="kt">int</span> <span class="n">ThisChar</span> <span class="o">=</span> <span class="n">LastChar</span><span class="p">;</span>
+  <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+  <span class="k">return</span> <span class="n">ThisChar</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Abstract Syntax Tree (aka Parse Tree)</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="k">namespace</span> <span class="p">{</span>
+<span class="c1">/// ExprAST - Base class for all expression nodes.</span>
+<span class="k">class</span> <span class="nc">ExprAST</span> <span class="p">{</span>
+<span class="nl">public:</span>
+  <span class="k">virtual</span> <span class="o">~</span><span class="n">ExprAST</span><span class="p">()</span> <span class="p">{}</span>
+  <span class="k">virtual</span> <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// NumberExprAST - Expression class for numeric literals like "1.0".</span>
+<span class="k">class</span> <span class="nc">NumberExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">double</span> <span class="n">Val</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">NumberExprAST</span><span class="p">(</span><span class="kt">double</span> <span class="n">val</span><span class="p">)</span> <span class="o">:</span> <span class="n">Val</span><span class="p">(</span><span class="n">val</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// VariableExprAST - Expression class for referencing a variable, like "a".</span>
+<span class="k">class</span> <span class="nc">VariableExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">VariableExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">name</span><span class="p">)</span> <span class="o">:</span> <span class="n">Name</span><span class="p">(</span><span class="n">name</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// UnaryExprAST - Expression class for a unary operator.</span>
+<span class="k">class</span> <span class="nc">UnaryExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">char</span> <span class="n">Opcode</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Operand</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">UnaryExprAST</span><span class="p">(</span><span class="kt">char</span> <span class="n">opcode</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">operand</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Opcode</span><span class="p">(</span><span class="n">opcode</span><span class="p">),</span> <span class="n">Operand</span><span class="p">(</span><span class="n">operand</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// BinaryExprAST - Expression class for a binary operator.</span>
+<span class="k">class</span> <span class="nc">BinaryExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">char</span> <span class="n">Op</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span><span class="p">,</span> <span class="o">*</span><span class="n">RHS</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">BinaryExprAST</span><span class="p">(</span><span class="kt">char</span> <span class="n">op</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">lhs</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">rhs</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Op</span><span class="p">(</span><span class="n">op</span><span class="p">),</span> <span class="n">LHS</span><span class="p">(</span><span class="n">lhs</span><span class="p">),</span> <span class="n">RHS</span><span class="p">(</span><span class="n">rhs</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// CallExprAST - Expression class for function calls.</span>
+<span class="k">class</span> <span class="nc">CallExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Callee</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="n">Args</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">CallExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">callee</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="o">&</span><span class="n">args</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Callee</span><span class="p">(</span><span class="n">callee</span><span class="p">),</span> <span class="n">Args</span><span class="p">(</span><span class="n">args</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// IfExprAST - Expression class for if/then/else.</span>
+<span class="k">class</span> <span class="nc">IfExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Cond</span><span class="p">,</span> <span class="o">*</span><span class="n">Then</span><span class="p">,</span> <span class="o">*</span><span class="n">Else</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">IfExprAST</span><span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">cond</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">then</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">_else</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Cond</span><span class="p">(</span><span class="n">cond</span><span class="p">),</span> <span class="n">Then</span><span class="p">(</span><span class="n">then</span><span class="p">),</span> <span class="n">Else</span><span class="p">(</span><span class="n">_else</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// ForExprAST - Expression class for for/in.</span>
+<span class="k">class</span> <span class="nc">ForExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">VarName</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Start</span><span class="p">,</span> <span class="o">*</span><span class="n">End</span><span class="p">,</span> <span class="o">*</span><span class="n">Step</span><span class="p">,</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">ForExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">varname</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">start</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">end</span><span class="p">,</span>
+             <span class="n">ExprAST</span> <span class="o">*</span><span class="n">step</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">VarName</span><span class="p">(</span><span class="n">varname</span><span class="p">),</span> <span class="n">Start</span><span class="p">(</span><span class="n">start</span><span class="p">),</span> <span class="n">End</span><span class="p">(</span><span class="n">end</span><span class="p">),</span> <span class="n">Step</span><span class="p">(</span><span class="n">step</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// PrototypeAST - This class represents the "prototype" for a function,</span>
+<span class="c1">/// which captures its name, and its argument names (thus implicitly the number</span>
+<span class="c1">/// of arguments the function takes), as well as if it is an operator.</span>
+<span class="k">class</span> <span class="nc">PrototypeAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">Args</span><span class="p">;</span>
+  <span class="kt">bool</span> <span class="n">isOperator</span><span class="p">;</span>
+  <span class="kt">unsigned</span> <span class="n">Precedence</span><span class="p">;</span> <span class="c1">// Precedence if a binary op.</span>
+<span class="nl">public:</span>
+  <span class="n">PrototypeAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">name</span><span class="p">,</span> <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="o">&</span><span class="n">args</span><span class="p">,</span>
+               <span class="kt">bool</span> <span class="n">isoperator</span> <span class="o">=</span> <span class="nb">false</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">prec</span> <span class="o">=</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Name</span><span class="p">(</span><span class="n">name</span><span class="p">),</span> <span class="n">Args</span><span class="p">(</span><span class="n">args</span><span class="p">),</span> <span class="n">isOperator</span><span class="p">(</span><span class="n">isoperator</span><span class="p">),</span> <span class="n">Precedence</span><span class="p">(</span><span class="n">prec</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="kt">bool</span> <span class="n">isUnaryOp</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">isOperator</span> <span class="o">&&</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">==</span> <span class="mi">1</span><span class="p">;</span> <span class="p">}</span>
+  <span class="kt">bool</span> <span class="n">isBinaryOp</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">isOperator</span> <span class="o">&&</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">==</span> <span class="mi">2</span><span class="p">;</span> <span class="p">}</span>
+
+  <span class="kt">char</span> <span class="n">getOperatorName</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span>
+    <span class="n">assert</span><span class="p">(</span><span class="n">isUnaryOp</span><span class="p">()</span> <span class="o">||</span> <span class="n">isBinaryOp</span><span class="p">());</span>
+    <span class="k">return</span> <span class="n">Name</span><span class="p">[</span><span class="n">Name</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">-</span> <span class="mi">1</span><span class="p">];</span>
+  <span class="p">}</span>
+
+  <span class="kt">unsigned</span> <span class="n">getBinaryPrecedence</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">Precedence</span><span class="p">;</span> <span class="p">}</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+
+<span class="c1">/// FunctionAST - This class represents a function definition itself.</span>
+<span class="k">class</span> <span class="nc">FunctionAST</span> <span class="p">{</span>
+  <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">FunctionAST</span><span class="p">(</span><span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">proto</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span> <span class="o">:</span> <span class="n">Proto</span><span class="p">(</span><span class="n">proto</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+<span class="p">}</span> <span class="c1">// end anonymous namespace</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Parser</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">/// CurTok/getNextToken - Provide a simple token buffer.  CurTok is the current</span>
+<span class="c1">/// token the parser is looking at.  getNextToken reads another token from the</span>
+<span class="c1">/// lexer and updates CurTok with its results.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="n">CurTok</span><span class="p">;</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">getNextToken</span><span class="p">()</span> <span class="p">{</span> <span class="k">return</span> <span class="n">CurTok</span> <span class="o">=</span> <span class="n">gettok</span><span class="p">();</span> <span class="p">}</span>
+
+<span class="c1">/// BinopPrecedence - This holds the precedence for each binary operator that is</span>
+<span class="c1">/// defined.</span>
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="kt">char</span><span class="p">,</span> <span class="kt">int</span><span class="o">></span> <span class="n">BinopPrecedence</span><span class="p">;</span>
+
+<span class="c1">/// GetTokPrecedence - Get the precedence of the pending binary operator token.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">GetTokPrecedence</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+    <span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
+
+  <span class="c1">// Make sure it's a declared binop.</span>
+  <span class="kt">int</span> <span class="n">TokPrec</span> <span class="o">=</span> <span class="n">BinopPrecedence</span><span class="p">[</span><span class="n">CurTok</span><span class="p">];</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><=</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
+  <span class="k">return</span> <span class="n">TokPrec</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// Error* - These are little helper functions for error handling.</span>
+<span class="n">ExprAST</span> <span class="o">*</span><span class="nf">Error</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Error: %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+<span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ErrorP</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+<span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ErrorF</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseExpression</span><span class="p">();</span>
+
+<span class="c1">/// identifierexpr</span>
+<span class="c1">///   ::= identifier</span>
+<span class="c1">///   ::= identifier '(' expression* ')'</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseIdentifierExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat identifier.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'('</span><span class="p">)</span> <span class="c1">// Simple variable ref.</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">VariableExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">);</span>
+
+  <span class="c1">// Call.</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat (</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="n">Args</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Arg</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+      <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Arg</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+      <span class="n">Args</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">Arg</span><span class="p">);</span>
+
+      <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">')'</span><span class="p">)</span>
+        <span class="k">break</span><span class="p">;</span>
+
+      <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span>
+        <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"Expected ')' or ',' in argument list"</span><span class="p">);</span>
+      <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Eat the ')'.</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">CallExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">,</span> <span class="n">Args</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// numberexpr ::= number</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseNumberExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Result</span> <span class="o">=</span> <span class="k">new</span> <span class="n">NumberExprAST</span><span class="p">(</span><span class="n">NumVal</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// consume the number</span>
+  <span class="k">return</span> <span class="n">Result</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// parenexpr ::= '(' expression ')'</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseParenExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat (.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">V</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">V</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected ')'"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat ).</span>
+  <span class="k">return</span> <span class="n">V</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// ifexpr ::= 'if' expression 'then' expression 'else' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseIfExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the if.</span>
+
+  <span class="c1">// condition.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Cond</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Cond</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_then</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected then"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the then</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Then</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Then</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_else</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected else"</span><span class="p">);</span>
+
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Else</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Else</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">IfExprAST</span><span class="p">(</span><span class="n">Cond</span><span class="p">,</span> <span class="n">Then</span><span class="p">,</span> <span class="n">Else</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseForExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the for.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected identifier after for"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat identifier.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'='</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected '=' after for"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat '='.</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Start</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Start</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected ',' after for start value"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">End</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">End</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// The step value is optional.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Step</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">','</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="n">Step</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Step</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_in</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected 'in' after for"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat 'in'.</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Body</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">ForExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">,</span> <span class="n">Start</span><span class="p">,</span> <span class="n">End</span><span class="p">,</span> <span class="n">Step</span><span class="p">,</span> <span class="n">Body</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// primary</span>
+<span class="c1">///   ::= identifierexpr</span>
+<span class="c1">///   ::= numberexpr</span>
+<span class="c1">///   ::= parenexpr</span>
+<span class="c1">///   ::= ifexpr</span>
+<span class="c1">///   ::= forexpr</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParsePrimary</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="nl">default:</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"unknown token when expecting an expression"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>:
+    <span class="k">return</span> <span class="n">ParseIdentifierExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_number</span>:
+    <span class="k">return</span> <span class="n">ParseNumberExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="sc">'('</span>:
+    <span class="k">return</span> <span class="n">ParseParenExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_if</span>:
+    <span class="k">return</span> <span class="n">ParseIfExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_for</span>:
+    <span class="k">return</span> <span class="n">ParseForExpr</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// unary</span>
+<span class="c1">///   ::= primary</span>
+<span class="c1">///   ::= '!' unary</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseUnary</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// If the current token is not an operator, it must be a primary expr.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="o">||</span> <span class="n">CurTok</span> <span class="o">==</span> <span class="sc">'('</span> <span class="o">||</span> <span class="n">CurTok</span> <span class="o">==</span> <span class="sc">','</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ParsePrimary</span><span class="p">();</span>
+
+  <span class="c1">// If this is a unary operator, read it.</span>
+  <span class="kt">int</span> <span class="n">Opc</span> <span class="o">=</span> <span class="n">CurTok</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">Operand</span> <span class="o">=</span> <span class="n">ParseUnary</span><span class="p">())</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">UnaryExprAST</span><span class="p">(</span><span class="n">Opc</span><span class="p">,</span> <span class="n">Operand</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// binoprhs</span>
+<span class="c1">///   ::= ('+' unary)*</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseBinOpRHS</span><span class="p">(</span><span class="kt">int</span> <span class="n">ExprPrec</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span><span class="p">)</span> <span class="p">{</span>
+  <span class="c1">// If this is a binop, find its precedence.</span>
+  <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+    <span class="kt">int</span> <span class="n">TokPrec</span> <span class="o">=</span> <span class="n">GetTokPrecedence</span><span class="p">();</span>
+
+    <span class="c1">// If this is a binop that binds at least as tightly as the current binop,</span>
+    <span class="c1">// consume it, otherwise we are done.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><</span> <span class="n">ExprPrec</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">LHS</span><span class="p">;</span>
+
+    <span class="c1">// Okay, we know this is a binop.</span>
+    <span class="kt">int</span> <span class="n">BinOp</span> <span class="o">=</span> <span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat binop</span>
+
+    <span class="c1">// Parse the unary expression after the binary operator.</span>
+    <span class="n">ExprAST</span> <span class="o">*</span><span class="n">RHS</span> <span class="o">=</span> <span class="n">ParseUnary</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">RHS</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+    <span class="c1">// If BinOp binds less tightly with RHS than the operator after RHS, let</span>
+    <span class="c1">// the pending operator take RHS as its LHS.</span>
+    <span class="kt">int</span> <span class="n">NextPrec</span> <span class="o">=</span> <span class="n">GetTokPrecedence</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><</span> <span class="n">NextPrec</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">RHS</span> <span class="o">=</span> <span class="n">ParseBinOpRHS</span><span class="p">(</span><span class="n">TokPrec</span> <span class="o">+</span> <span class="mi">1</span><span class="p">,</span> <span class="n">RHS</span><span class="p">);</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">RHS</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+
+    <span class="c1">// Merge LHS/RHS.</span>
+    <span class="n">LHS</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BinaryExprAST</span><span class="p">(</span><span class="n">BinOp</span><span class="p">,</span> <span class="n">LHS</span><span class="p">,</span> <span class="n">RHS</span><span class="p">);</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// expression</span>
+<span class="c1">///   ::= unary binoprhs</span>
+<span class="c1">///</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseExpression</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span> <span class="o">=</span> <span class="n">ParseUnary</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">LHS</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="n">ParseBinOpRHS</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">LHS</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// prototype</span>
+<span class="c1">///   ::= id '(' id* ')'</span>
+<span class="c1">///   ::= binary LETTER number? (id, id)</span>
+<span class="c1">///   ::= unary LETTER (id)</span>
+<span class="k">static</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ParsePrototype</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">FnName</span><span class="p">;</span>
+
+  <span class="kt">unsigned</span> <span class="n">Kind</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="c1">// 0 = identifier, 1 = unary, 2 = binary.</span>
+  <span class="kt">unsigned</span> <span class="n">BinaryPrecedence</span> <span class="o">=</span> <span class="mi">30</span><span class="p">;</span>
+
+  <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="nl">default:</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected function name in prototype"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>:
+    <span class="n">FnName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_unary</span>:
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+      <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected unary operator"</span><span class="p">);</span>
+    <span class="n">FnName</span> <span class="o">=</span> <span class="s">"unary"</span><span class="p">;</span>
+    <span class="n">FnName</span> <span class="o">+=</span> <span class="p">(</span><span class="kt">char</span><span class="p">)</span><span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_binary</span>:
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+      <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected binary operator"</span><span class="p">);</span>
+    <span class="n">FnName</span> <span class="o">=</span> <span class="s">"binary"</span><span class="p">;</span>
+    <span class="n">FnName</span> <span class="o">+=</span> <span class="p">(</span><span class="kt">char</span><span class="p">)</span><span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+
+    <span class="c1">// Read the precedence if present.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="n">tok_number</span><span class="p">)</span> <span class="p">{</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">NumVal</span> <span class="o"><</span> <span class="mi">1</span> <span class="o">||</span> <span class="n">NumVal</span> <span class="o">></span> <span class="mi">100</span><span class="p">)</span>
+        <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Invalid precedecnce: must be 1..100"</span><span class="p">);</span>
+      <span class="n">BinaryPrecedence</span> <span class="o">=</span> <span class="p">(</span><span class="kt">unsigned</span><span class="p">)</span><span class="n">NumVal</span><span class="p">;</span>
+      <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="p">}</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'('</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected '(' in prototype"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">ArgNames</span><span class="p">;</span>
+  <span class="k">while</span> <span class="p">(</span><span class="n">getNextToken</span><span class="p">()</span> <span class="o">==</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="n">ArgNames</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">IdentifierStr</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected ')' in prototype"</span><span class="p">);</span>
+
+  <span class="c1">// success.</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat ')'.</span>
+
+  <span class="c1">// Verify right number of names for operator.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Kind</span> <span class="o">&&</span> <span class="n">ArgNames</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Kind</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Invalid number of operands for operator"</span><span class="p">);</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">PrototypeAST</span><span class="p">(</span><span class="n">FnName</span><span class="p">,</span> <span class="n">ArgNames</span><span class="p">,</span> <span class="n">Kind</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">BinaryPrecedence</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// definition ::= 'def' prototype expression</span>
+<span class="k">static</span> <span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ParseDefinition</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat def.</span>
+  <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span> <span class="o">=</span> <span class="n">ParsePrototype</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Proto</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">E</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">())</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">FunctionAST</span><span class="p">(</span><span class="n">Proto</span><span class="p">,</span> <span class="n">E</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// toplevelexpr ::= expression</span>
+<span class="k">static</span> <span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ParseTopLevelExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">E</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">())</span> <span class="p">{</span>
+    <span class="c1">// Make an anonymous proto.</span>
+    <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span> <span class="o">=</span> <span class="k">new</span> <span class="n">PrototypeAST</span><span class="p">(</span><span class="s">""</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="p">());</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">FunctionAST</span><span class="p">(</span><span class="n">Proto</span><span class="p">,</span> <span class="n">E</span><span class="p">);</span>
+  <span class="p">}</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// external ::= 'extern' prototype</span>
+<span class="k">static</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ParseExtern</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat extern.</span>
+  <span class="k">return</span> <span class="n">ParsePrototype</span><span class="p">();</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Code Generation</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="k">static</span> <span class="n">Module</span> <span class="o">*</span><span class="n">TheModule</span><span class="p">;</span>
+<span class="k">static</span> <span class="n">IRBuilder</span><span class="o"><></span> <span class="n">Builder</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">());</span>
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">Value</span> <span class="o">*></span> <span class="n">NamedValues</span><span class="p">;</span>
+<span class="k">static</span> <span class="n">legacy</span><span class="o">::</span><span class="n">FunctionPassManager</span> <span class="o">*</span><span class="n">TheFPM</span><span class="p">;</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="nf">ErrorV</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">NumberExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">return</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="n">Val</span><span class="p">));</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">VariableExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Look this variable up in the function.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">V</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">Name</span><span class="p">];</span>
+  <span class="k">return</span> <span class="n">V</span> <span class="o">?</span> <span class="n">V</span> <span class="o">:</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown variable name"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">UnaryExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">OperandV</span> <span class="o">=</span> <span class="n">Operand</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">OperandV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">(</span><span class="s">"unary"</span><span class="p">)</span> <span class="o">+</span> <span class="n">Opcode</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">F</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown unary operator"</span><span class="p">);</span>
+
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">F</span><span class="p">,</span> <span class="n">OperandV</span><span class="p">,</span> <span class="s">"unop"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">BinaryExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">L</span> <span class="o">=</span> <span class="n">LHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">R</span> <span class="o">=</span> <span class="n">RHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">L</span> <span class="o">==</span> <span class="mi">0</span> <span class="o">||</span> <span class="n">R</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">switch</span> <span class="p">(</span><span class="n">Op</span><span class="p">)</span> <span class="p">{</span>
+  <span class="k">case</span> <span class="sc">'+'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFAdd</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"addtmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'-'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFSub</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"subtmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'*'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFMul</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"multmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'<'</span>:
+    <span class="n">L</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpULT</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"cmptmp"</span><span class="p">);</span>
+    <span class="c1">// Convert bool 0/1 to double 0.0 or 1.0</span>
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateUIToFP</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span>
+                                <span class="s">"booltmp"</span><span class="p">);</span>
+  <span class="nl">default:</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="c1">// If it wasn't a builtin binary operator, it must be a user defined one. Emit</span>
+  <span class="c1">// a call to it.</span>
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">(</span><span class="s">"binary"</span><span class="p">)</span> <span class="o">+</span> <span class="n">Op</span><span class="p">);</span>
+  <span class="n">assert</span><span class="p">(</span><span class="n">F</span> <span class="o">&&</span> <span class="s">"binary operator not found!"</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Ops</span><span class="p">[]</span> <span class="o">=</span> <span class="p">{</span> <span class="n">L</span><span class="p">,</span> <span class="n">R</span> <span class="p">};</span>
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">F</span><span class="p">,</span> <span class="n">Ops</span><span class="p">,</span> <span class="s">"binop"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">CallExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Look up the name in the global module table.</span>
+  <span class="n">Function</span> <span class="o">*</span><span class="n">CalleeF</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">Callee</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CalleeF</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown function referenced"</span><span class="p">);</span>
+
+  <span class="c1">// If argument mismatch error.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CalleeF</span><span class="o">-></span><span class="n">arg_size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">())</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Incorrect # arguments passed"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">Value</span> <span class="o">*></span> <span class="n">ArgsV</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">ArgsV</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">Args</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="o">-></span><span class="n">Codegen</span><span class="p">());</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">ArgsV</span><span class="p">.</span><span class="n">back</span><span class="p">()</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">CalleeF</span><span class="p">,</span> <span class="n">ArgsV</span><span class="p">,</span> <span class="s">"calltmp"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">IfExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">CondV</span> <span class="o">=</span> <span class="n">Cond</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CondV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Convert condition to a bool by comparing equal to 0.0.</span>
+  <span class="n">CondV</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpONE</span><span class="p">(</span>
+      <span class="n">CondV</span><span class="p">,</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">)),</span> <span class="s">"ifcond"</span><span class="p">);</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+
+  <span class="c1">// Create blocks for the then and else cases.  Insert the 'then' block at the</span>
+  <span class="c1">// end of the function.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">ThenBB</span> <span class="o">=</span>
+      <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"then"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">ElseBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"else"</span><span class="p">);</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">MergeBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"ifcont"</span><span class="p">);</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCondBr</span><span class="p">(</span><span class="n">CondV</span><span class="p">,</span> <span class="n">ThenBB</span><span class="p">,</span> <span class="n">ElseBB</span><span class="p">);</span>
+
+  <span class="c1">// Emit then value.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">ThenBB</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">ThenV</span> <span class="o">=</span> <span class="n">Then</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ThenV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="c1">// Codegen of 'Then' can change the current block, update ThenBB for the PHI.</span>
+  <span class="n">ThenBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+
+  <span class="c1">// Emit else block.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">getBasicBlockList</span><span class="p">().</span><span class="n">push_back</span><span class="p">(</span><span class="n">ElseBB</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">ElseBB</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">ElseV</span> <span class="o">=</span> <span class="n">Else</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ElseV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="c1">// Codegen of 'Else' can change the current block, update ElseBB for the PHI.</span>
+  <span class="n">ElseBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+
+  <span class="c1">// Emit merge block.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">getBasicBlockList</span><span class="p">().</span><span class="n">push_back</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="n">PHINode</span> <span class="o">*</span><span class="n">PN</span> <span class="o">=</span>
+      <span class="n">Builder</span><span class="p">.</span><span class="n">CreatePHI</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="mi">2</span><span class="p">,</span> <span class="s">"iftmp"</span><span class="p">);</span>
+
+  <span class="n">PN</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">ThenV</span><span class="p">,</span> <span class="n">ThenBB</span><span class="p">);</span>
+  <span class="n">PN</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">ElseV</span><span class="p">,</span> <span class="n">ElseBB</span><span class="p">);</span>
+  <span class="k">return</span> <span class="n">PN</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">ForExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Output this as:</span>
+  <span class="c1">//   ...</span>
+  <span class="c1">//   start = startexpr</span>
+  <span class="c1">//   goto loop</span>
+  <span class="c1">// loop:</span>
+  <span class="c1">//   variable = phi [start, loopheader], [nextvariable, loopend]</span>
+  <span class="c1">//   ...</span>
+  <span class="c1">//   bodyexpr</span>
+  <span class="c1">//   ...</span>
+  <span class="c1">// loopend:</span>
+  <span class="c1">//   step = stepexpr</span>
+  <span class="c1">//   nextvariable = variable + step</span>
+  <span class="c1">//   endcond = endexpr</span>
+  <span class="c1">//   br endcond, loop, endloop</span>
+  <span class="c1">// outloop:</span>
+
+  <span class="c1">// Emit the start code first, without 'variable' in scope.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">StartVal</span> <span class="o">=</span> <span class="n">Start</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">StartVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Make the new basic block for the loop header, inserting after current</span>
+  <span class="c1">// block.</span>
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">PreheaderBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">LoopBB</span> <span class="o">=</span>
+      <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"loop"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+
+  <span class="c1">// Insert an explicit fall through from the current block to the LoopBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">LoopBB</span><span class="p">);</span>
+
+  <span class="c1">// Start insertion in LoopBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">LoopBB</span><span class="p">);</span>
+
+  <span class="c1">// Start the PHI node with an entry for Start.</span>
+  <span class="n">PHINode</span> <span class="o">*</span><span class="n">Variable</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreatePHI</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span>
+                                        <span class="mi">2</span><span class="p">,</span> <span class="n">VarName</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+  <span class="n">Variable</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">StartVal</span><span class="p">,</span> <span class="n">PreheaderBB</span><span class="p">);</span>
+
+  <span class="c1">// Within the loop, the variable is defined equal to the PHI node.  If it</span>
+  <span class="c1">// shadows an existing variable, we have to restore it, so save it now.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">OldVal</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">];</span>
+  <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">Variable</span><span class="p">;</span>
+
+  <span class="c1">// Emit the body of the loop.  This, like any other expr, can change the</span>
+  <span class="c1">// current BB.  Note that we ignore the value computed by the body, but don't</span>
+  <span class="c1">// allow an error.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">()</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Emit the step value.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">StepVal</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Step</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">StepVal</span> <span class="o">=</span> <span class="n">Step</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">StepVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// If not specified, use 1.0.</span>
+    <span class="n">StepVal</span> <span class="o">=</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">1.0</span><span class="p">));</span>
+  <span class="p">}</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">NextVar</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFAdd</span><span class="p">(</span><span class="n">Variable</span><span class="p">,</span> <span class="n">StepVal</span><span class="p">,</span> <span class="s">"nextvar"</span><span class="p">);</span>
+
+  <span class="c1">// Compute the end condition.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">EndCond</span> <span class="o">=</span> <span class="n">End</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">EndCond</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">EndCond</span><span class="p">;</span>
+
+  <span class="c1">// Convert condition to a bool by comparing equal to 0.0.</span>
+  <span class="n">EndCond</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpONE</span><span class="p">(</span>
+      <span class="n">EndCond</span><span class="p">,</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">)),</span> <span class="s">"loopcond"</span><span class="p">);</span>
+
+  <span class="c1">// Create the "after loop" block and insert it.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">LoopEndBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">AfterBB</span> <span class="o">=</span>
+      <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"afterloop"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+
+  <span class="c1">// Insert the conditional branch into the end of LoopEndBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCondBr</span><span class="p">(</span><span class="n">EndCond</span><span class="p">,</span> <span class="n">LoopBB</span><span class="p">,</span> <span class="n">AfterBB</span><span class="p">);</span>
+
+  <span class="c1">// Any new code will be inserted in AfterBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">AfterBB</span><span class="p">);</span>
+
+  <span class="c1">// Add a new entry to the PHI node for the backedge.</span>
+  <span class="n">Variable</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">NextVar</span><span class="p">,</span> <span class="n">LoopEndBB</span><span class="p">);</span>
+
+  <span class="c1">// Restore the unshadowed variable.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">OldVal</span><span class="p">)</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">OldVal</span><span class="p">;</span>
+  <span class="k">else</span>
+    <span class="n">NamedValues</span><span class="p">.</span><span class="n">erase</span><span class="p">(</span><span class="n">VarName</span><span class="p">);</span>
+
+  <span class="c1">// for expr always returns 0.0.</span>
+  <span class="k">return</span> <span class="n">Constant</span><span class="o">::</span><span class="n">getNullValue</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()));</span>
+<span class="p">}</span>
+
+<span class="n">Function</span> <span class="o">*</span><span class="n">PrototypeAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Make the function type:  double(double,double) etc.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">Type</span> <span class="o">*></span> <span class="n">Doubles</span><span class="p">(</span><span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">(),</span>
+                              <span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()));</span>
+  <span class="n">FunctionType</span> <span class="o">*</span><span class="n">FT</span> <span class="o">=</span>
+      <span class="n">FunctionType</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="n">Doubles</span><span class="p">,</span> <span class="nb">false</span><span class="p">);</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span>
+      <span class="n">Function</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">FT</span><span class="p">,</span> <span class="n">Function</span><span class="o">::</span><span class="n">ExternalLinkage</span><span class="p">,</span> <span class="n">Name</span><span class="p">,</span> <span class="n">TheModule</span><span class="p">);</span>
+
+  <span class="c1">// If F conflicted, there was already something named 'Name'.  If it has a</span>
+  <span class="c1">// body, don't allow redefinition or reextern.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">F</span><span class="o">-></span><span class="n">getName</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Name</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Delete the one we just made and get the existing one.</span>
+    <span class="n">F</span><span class="o">-></span><span class="n">eraseFromParent</span><span class="p">();</span>
+    <span class="n">F</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">Name</span><span class="p">);</span>
+
+    <span class="c1">// If F already has a body, reject this.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">F</span><span class="o">-></span><span class="n">empty</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">ErrorF</span><span class="p">(</span><span class="s">"redefinition of function"</span><span class="p">);</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+
+    <span class="c1">// If F took a different number of args, reject.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">F</span><span class="o">-></span><span class="n">arg_size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">ErrorF</span><span class="p">(</span><span class="s">"redefinition of function with different # args"</span><span class="p">);</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Set names for all arguments.</span>
+  <span class="kt">unsigned</span> <span class="n">Idx</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="n">Function</span><span class="o">::</span><span class="n">arg_iterator</span> <span class="n">AI</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">arg_begin</span><span class="p">();</span> <span class="n">Idx</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span>
+       <span class="o">++</span><span class="n">AI</span><span class="p">,</span> <span class="o">++</span><span class="n">Idx</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">AI</span><span class="o">-></span><span class="n">setName</span><span class="p">(</span><span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]);</span>
+
+    <span class="c1">// Add arguments to variable symbol table.</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]]</span> <span class="o">=</span> <span class="n">AI</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">return</span> <span class="n">F</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Function</span> <span class="o">*</span><span class="n">FunctionAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">NamedValues</span><span class="p">.</span><span class="n">clear</span><span class="p">();</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Proto</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">TheFunction</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// If this is an operator, install it.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Proto</span><span class="o">-></span><span class="n">isBinaryOp</span><span class="p">())</span>
+    <span class="n">BinopPrecedence</span><span class="p">[</span><span class="n">Proto</span><span class="o">-></span><span class="n">getOperatorName</span><span class="p">()]</span> <span class="o">=</span> <span class="n">Proto</span><span class="o">-></span><span class="n">getBinaryPrecedence</span><span class="p">();</span>
+
+  <span class="c1">// Create a new basic block to start insertion into.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">BB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"entry"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">BB</span><span class="p">);</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">Value</span> <span class="o">*</span><span class="n">RetVal</span> <span class="o">=</span> <span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+    <span class="c1">// Finish off the function.</span>
+    <span class="n">Builder</span><span class="p">.</span><span class="n">CreateRet</span><span class="p">(</span><span class="n">RetVal</span><span class="p">);</span>
+
+    <span class="c1">// Validate the generated code, checking for consistency.</span>
+    <span class="n">verifyFunction</span><span class="p">(</span><span class="o">*</span><span class="n">TheFunction</span><span class="p">);</span>
+
+    <span class="c1">// Optimize the function.</span>
+    <span class="n">TheFPM</span><span class="o">-></span><span class="n">run</span><span class="p">(</span><span class="o">*</span><span class="n">TheFunction</span><span class="p">);</span>
+
+    <span class="k">return</span> <span class="n">TheFunction</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Error reading body, remove function.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">eraseFromParent</span><span class="p">();</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">Proto</span><span class="o">-></span><span class="n">isBinaryOp</span><span class="p">())</span>
+    <span class="n">BinopPrecedence</span><span class="p">.</span><span class="n">erase</span><span class="p">(</span><span class="n">Proto</span><span class="o">-></span><span class="n">getOperatorName</span><span class="p">());</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Top-Level parsing and JIT Driver</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="k">static</span> <span class="n">ExecutionEngine</span> <span class="o">*</span><span class="n">TheExecutionEngine</span><span class="p">;</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleDefinition</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">FunctionAST</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">ParseDefinition</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">LF</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Read function definition:"</span><span class="p">);</span>
+      <span class="n">LF</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleExtern</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">P</span> <span class="o">=</span> <span class="n">ParseExtern</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">P</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Read extern: "</span><span class="p">);</span>
+      <span class="n">F</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleTopLevelExpression</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Evaluate a top-level expression into an anonymous function.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">FunctionAST</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">ParseTopLevelExpr</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">LF</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">finalizeObject</span><span class="p">();</span>
+      <span class="c1">// JIT the function, returning a function pointer.</span>
+      <span class="kt">void</span> <span class="o">*</span><span class="n">FPtr</span> <span class="o">=</span> <span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">getPointerToFunction</span><span class="p">(</span><span class="n">LF</span><span class="p">);</span>
+
+      <span class="c1">// Cast it to the right type (takes no arguments, returns a double) so we</span>
+      <span class="c1">// can call it as a native function.</span>
+      <span class="kt">double</span> <span class="p">(</span><span class="o">*</span><span class="n">FP</span><span class="p">)()</span> <span class="o">=</span> <span class="p">(</span><span class="kt">double</span> <span class="p">(</span><span class="o">*</span><span class="p">)())(</span><span class="kt">intptr_t</span><span class="p">)</span><span class="n">FPtr</span><span class="p">;</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Evaluated to %f</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">FP</span><span class="p">());</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// top ::= definition | external | expression | ';'</span>
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">MainLoop</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"ready> "</span><span class="p">);</span>
+    <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">case</span> <span class="n">tok_eof</span>:
+      <span class="k">return</span><span class="p">;</span>
+    <span class="k">case</span> <span class="sc">';'</span>:
+      <span class="n">getNextToken</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span> <span class="c1">// ignore top-level semicolons.</span>
+    <span class="k">case</span> <span class="n">tok_def</span>:
+      <span class="n">HandleDefinition</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="k">case</span> <span class="n">tok_extern</span>:
+      <span class="n">HandleExtern</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="nl">default:</span>
+      <span class="n">HandleTopLevelExpression</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// "Library" functions that can be "extern'd" from user code.</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">/// putchard - putchar that takes a double and returns 0.</span>
+<span class="k">extern</span> <span class="s">"C"</span> <span class="kt">double</span> <span class="n">putchard</span><span class="p">(</span><span class="kt">double</span> <span class="n">X</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">putchar</span><span class="p">((</span><span class="kt">char</span><span class="p">)</span><span class="n">X</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// printd - printf that takes a double prints it as "%f\n", returning 0.</span>
+<span class="k">extern</span> <span class="s">"C"</span> <span class="kt">double</span> <span class="n">printd</span><span class="p">(</span><span class="kt">double</span> <span class="n">X</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">printf</span><span class="p">(</span><span class="s">"%f</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">X</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Main driver code.</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="kt">int</span> <span class="n">main</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">InitializeNativeTarget</span><span class="p">();</span>
+  <span class="n">InitializeNativeTargetAsmPrinter</span><span class="p">();</span>
+  <span class="n">InitializeNativeTargetAsmParser</span><span class="p">();</span>
+  <span class="n">LLVMContext</span> <span class="o">&</span><span class="n">Context</span> <span class="o">=</span> <span class="n">getGlobalContext</span><span class="p">();</span>
+
+  <span class="c1">// Install standard binary operators.</span>
+  <span class="c1">// 1 is lowest precedence.</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'<'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'+'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'-'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'*'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">40</span><span class="p">;</span> <span class="c1">// highest.</span>
+
+  <span class="c1">// Prime the first token.</span>
+  <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"ready> "</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="c1">// Make the module, which holds all the code.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">unique_ptr</span><span class="o"><</span><span class="n">Module</span><span class="o">></span> <span class="n">Owner</span> <span class="o">=</span> <span class="n">make_unique</span><span class="o"><</span><span class="n">Module</span><span class="o">></span><span class="p">(</span><span class="s">"my cool jit"</span><span class="p">,</span> <span class="n">Context</span><span class="p">);</span>
+  <span class="n">TheModule</span> <span class="o">=</span> <span class="n">Owner</span><span class="p">.</span><span class="n">get</span><span class="p">();</span>
+
+  <span class="c1">// Create the JIT.  This takes ownership of the module.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">ErrStr</span><span class="p">;</span>
+  <span class="n">TheExecutionEngine</span> <span class="o">=</span>
+      <span class="n">EngineBuilder</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">move</span><span class="p">(</span><span class="n">Owner</span><span class="p">))</span>
+          <span class="p">.</span><span class="n">setErrorStr</span><span class="p">(</span><span class="o">&</span><span class="n">ErrStr</span><span class="p">)</span>
+          <span class="p">.</span><span class="n">setMCJITMemoryManager</span><span class="p">(</span><span class="n">llvm</span><span class="o">::</span><span class="n">make_unique</span><span class="o"><</span><span class="n">SectionMemoryManager</span><span class="o">></span><span class="p">())</span>
+          <span class="p">.</span><span class="n">create</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">TheExecutionEngine</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Could not create ExecutionEngine: %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">ErrStr</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+    <span class="n">exit</span><span class="p">(</span><span class="mi">1</span><span class="p">);</span>
+  <span class="p">}</span>
+
+  <span class="n">legacy</span><span class="o">::</span><span class="n">FunctionPassManager</span> <span class="n">OurFPM</span><span class="p">(</span><span class="n">TheModule</span><span class="p">);</span>
+
+  <span class="c1">// Set up the optimizer pipeline.  Start with registering info about how the</span>
+  <span class="c1">// target lays out data structures.</span>
+  <span class="n">TheModule</span><span class="o">-></span><span class="n">setDataLayout</span><span class="p">(</span><span class="o">*</span><span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">getDataLayout</span><span class="p">());</span>
+  <span class="c1">// Provide basic AliasAnalysis support for GVN.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createBasicAliasAnalysisPass</span><span class="p">());</span>
+  <span class="c1">// Do simple "peephole" optimizations and bit-twiddling optzns.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createInstructionCombiningPass</span><span class="p">());</span>
+  <span class="c1">// Reassociate expressions.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createReassociatePass</span><span class="p">());</span>
+  <span class="c1">// Eliminate Common SubExpressions.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createGVNPass</span><span class="p">());</span>
+  <span class="c1">// Simplify the control flow graph (deleting unreachable blocks, etc).</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createCFGSimplificationPass</span><span class="p">());</span>
+
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">doInitialization</span><span class="p">();</span>
+
+  <span class="c1">// Set the global so the code gen can use this.</span>
+  <span class="n">TheFPM</span> <span class="o">=</span> <span class="o">&</span><span class="n">OurFPM</span><span class="p">;</span>
+
+  <span class="c1">// Run the main "interpreter loop" now.</span>
+  <span class="n">MainLoop</span><span class="p">();</span>
+
+  <span class="n">TheFPM</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Print out all of the generated code.</span>
+  <span class="n">TheModule</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p><a class="reference external" href="LangImpl7.html">Next: Extending the language: mutable variables / SSA
+construction</a></p>
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+  <div class="section" id="kaleidoscope-extending-the-language-mutable-variables">
+<h1>7. Kaleidoscope: Extending the Language: Mutable Variables<a class="headerlink" href="#kaleidoscope-extending-the-language-mutable-variables" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#chapter-7-introduction" id="id2">Chapter 7 Introduction</a></li>
+<li><a class="reference internal" href="#why-is-this-a-hard-problem" id="id3">Why is this a hard problem?</a></li>
+<li><a class="reference internal" href="#memory-in-llvm" id="id4">Memory in LLVM</a></li>
+<li><a class="reference internal" href="#mutable-variables-in-kaleidoscope" id="id5">Mutable Variables in Kaleidoscope</a></li>
+<li><a class="reference internal" href="#adjusting-existing-variables-for-mutation" id="id6">Adjusting Existing Variables for Mutation</a></li>
+<li><a class="reference internal" href="#new-assignment-operator" id="id7">New Assignment Operator</a></li>
+<li><a class="reference internal" href="#user-defined-local-variables" id="id8">User-defined Local Variables</a></li>
+<li><a class="reference internal" href="#id1" id="id9">Full Code Listing</a></li>
+</ul>
+</div>
+<div class="section" id="chapter-7-introduction">
+<h2><a class="toc-backref" href="#id2">7.1. Chapter 7 Introduction</a><a class="headerlink" href="#chapter-7-introduction" title="Permalink to this headline">¶</a></h2>
+<p>Welcome to Chapter 7 of the “<a class="reference external" href="index.html">Implementing a language with
+LLVM</a>” tutorial. In chapters 1 through 6, we’ve built a
+very respectable, albeit simple, <a class="reference external" href="http://en.wikipedia.org/wiki/Functional_programming">functional programming
+language</a>. In our
+journey, we learned some parsing techniques, how to build and represent
+an AST, how to build LLVM IR, and how to optimize the resultant code as
+well as JIT compile it.</p>
+<p>While Kaleidoscope is interesting as a functional language, the fact
+that it is functional makes it “too easy” to generate LLVM IR for it. In
+particular, a functional language makes it very easy to build LLVM IR
+directly in <a class="reference external" href="http://en.wikipedia.org/wiki/Static_single_assignment_form">SSA
+form</a>.
+Since LLVM requires that the input code be in SSA form, this is a very
+nice property and it is often unclear to newcomers how to generate code
+for an imperative language with mutable variables.</p>
+<p>The short (and happy) summary of this chapter is that there is no need
+for your front-end to build SSA form: LLVM provides highly tuned and
+well tested support for this, though the way it works is a bit
+unexpected for some.</p>
+</div>
+<div class="section" id="why-is-this-a-hard-problem">
+<h2><a class="toc-backref" href="#id3">7.2. Why is this a hard problem?</a><a class="headerlink" href="#why-is-this-a-hard-problem" title="Permalink to this headline">¶</a></h2>
+<p>To understand why mutable variables cause complexities in SSA
+construction, consider this extremely simple C example:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="kt">int</span> <span class="n">G</span><span class="p">,</span> <span class="n">H</span><span class="p">;</span>
+<span class="kt">int</span> <span class="nf">test</span><span class="p">(</span><span class="kt">_Bool</span> <span class="n">Condition</span><span class="p">)</span> <span class="p">{</span>
+  <span class="kt">int</span> <span class="n">X</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Condition</span><span class="p">)</span>
+    <span class="n">X</span> <span class="o">=</span> <span class="n">G</span><span class="p">;</span>
+  <span class="k">else</span>
+    <span class="n">X</span> <span class="o">=</span> <span class="n">H</span><span class="p">;</span>
+  <span class="k">return</span> <span class="n">X</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>In this case, we have the variable “X”, whose value depends on the path
+executed in the program. Because there are two different possible values
+for X before the return instruction, a PHI node is inserted to merge the
+two values. The LLVM IR that we want for this example looks like this:</p>
+<div class="highlight-llvm"><div class="highlight"><pre><span class="vg">@G</span> <span class="p">=</span> <span class="k">weak</span> <span class="k">global</span> <span class="k">i32</span> <span class="m">0</span>   <span class="c">; type of @G is i32*</span>
+<span class="vg">@H</span> <span class="p">=</span> <span class="k">weak</span> <span class="k">global</span> <span class="k">i32</span> <span class="m">0</span>   <span class="c">; type of @H is i32*</span>
+
+<span class="k">define</span> <span class="k">i32</span> <span class="vg">@test</span><span class="p">(</span><span class="k">i1</span> <span class="nv">%Condition</span><span class="p">)</span> <span class="p">{</span>
+<span class="nl">entry:</span>
+  <span class="k">br</span> <span class="k">i1</span> <span class="nv">%Condition</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%cond_true</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%cond_false</span>
+
+<span class="nl">cond_true:</span>
+  <span class="nv">%X.0</span> <span class="p">=</span> <span class="k">load</span> <span class="k">i32</span><span class="p">*</span> <span class="vg">@G</span>
+  <span class="k">br</span> <span class="kt">label</span> <span class="nv">%cond_next</span>
+
+<span class="nl">cond_false:</span>
+  <span class="nv">%X.1</span> <span class="p">=</span> <span class="k">load</span> <span class="k">i32</span><span class="p">*</span> <span class="vg">@H</span>
+  <span class="k">br</span> <span class="kt">label</span> <span class="nv">%cond_next</span>
+
+<span class="nl">cond_next:</span>
+  <span class="nv">%X.2</span> <span class="p">=</span> <span class="k">phi</span> <span class="k">i32</span> <span class="p">[</span> <span class="nv">%X.1</span><span class="p">,</span> <span class="nv">%cond_false</span> <span class="p">],</span> <span class="p">[</span> <span class="nv">%X.0</span><span class="p">,</span> <span class="nv">%cond_true</span> <span class="p">]</span>
+  <span class="k">ret</span> <span class="k">i32</span> <span class="nv">%X.2</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>In this example, the loads from the G and H global variables are
+explicit in the LLVM IR, and they live in the then/else branches of the
+if statement (cond_true/cond_false). In order to merge the incoming
+values, the X.2 phi node in the cond_next block selects the right value
+to use based on where control flow is coming from: if control flow comes
+from the cond_false block, X.2 gets the value of X.1. Alternatively, if
+control flow comes from cond_true, it gets the value of X.0. The intent
+of this chapter is not to explain the details of SSA form. For more
+information, see one of the many <a class="reference external" href="http://en.wikipedia.org/wiki/Static_single_assignment_form">online
+references</a>.</p>
+<p>The question for this article is “who places the phi nodes when lowering
+assignments to mutable variables?”. The issue here is that LLVM
+<em>requires</em> that its IR be in SSA form: there is no “non-ssa” mode for
+it. However, SSA construction requires non-trivial algorithms and data
+structures, so it is inconvenient and wasteful for every front-end to
+have to reproduce this logic.</p>
+</div>
+<div class="section" id="memory-in-llvm">
+<h2><a class="toc-backref" href="#id4">7.3. Memory in LLVM</a><a class="headerlink" href="#memory-in-llvm" title="Permalink to this headline">¶</a></h2>
+<p>The ‘trick’ here is that while LLVM does require all register values to
+be in SSA form, it does not require (or permit) memory objects to be in
+SSA form. In the example above, note that the loads from G and H are
+direct accesses to G and H: they are not renamed or versioned. This
+differs from some other compiler systems, which do try to version memory
+objects. In LLVM, instead of encoding dataflow analysis of memory into
+the LLVM IR, it is handled with <a class="reference external" href="../WritingAnLLVMPass.html">Analysis
+Passes</a> which are computed on demand.</p>
+<p>With this in mind, the high-level idea is that we want to make a stack
+variable (which lives in memory, because it is on the stack) for each
+mutable object in a function. To take advantage of this trick, we need
+to talk about how LLVM represents stack variables.</p>
+<p>In LLVM, all memory accesses are explicit with load/store instructions,
+and it is carefully designed not to have (or need) an “address-of”
+operator. Notice how the type of the @G/@H global variables is actually
+“i32*” even though the variable is defined as “i32”. What this means is
+that @G defines <em>space</em> for an i32 in the global data area, but its
+<em>name</em> actually refers to the address for that space. Stack variables
+work the same way, except that instead of being declared with global
+variable definitions, they are declared with the <a class="reference external" href="../LangRef.html#i_alloca">LLVM alloca
+instruction</a>:</p>
+<div class="highlight-llvm"><div class="highlight"><pre><span class="k">define</span> <span class="k">i32</span> <span class="vg">@example</span><span class="p">()</span> <span class="p">{</span>
+<span class="nl">entry:</span>
+  <span class="nv">%X</span> <span class="p">=</span> <span class="k">alloca</span> <span class="k">i32</span>           <span class="c">; type of %X is i32*.</span>
+  <span class="p">...</span>
+  <span class="nv">%tmp</span> <span class="p">=</span> <span class="k">load</span> <span class="k">i32</span><span class="p">*</span> <span class="nv">%X</span>       <span class="c">; load the stack value %X from the stack.</span>
+  <span class="nv">%tmp2</span> <span class="p">=</span> <span class="k">add</span> <span class="k">i32</span> <span class="nv">%tmp</span><span class="p">,</span> <span class="m">1</span>   <span class="c">; increment it</span>
+  <span class="k">store</span> <span class="k">i32</span> <span class="nv">%tmp2</span><span class="p">,</span> <span class="k">i32</span><span class="p">*</span> <span class="nv">%X</span>  <span class="c">; store it back</span>
+  <span class="p">...</span>
+</pre></div>
+</div>
+<p>This code shows an example of how you can declare and manipulate a stack
+variable in the LLVM IR. Stack memory allocated with the alloca
+instruction is fully general: you can pass the address of the stack slot
+to functions, you can store it in other variables, etc. In our example
+above, we could rewrite the example to use the alloca technique to avoid
+using a PHI node:</p>
+<div class="highlight-llvm"><div class="highlight"><pre><span class="vg">@G</span> <span class="p">=</span> <span class="k">weak</span> <span class="k">global</span> <span class="k">i32</span> <span class="m">0</span>   <span class="c">; type of @G is i32*</span>
+<span class="vg">@H</span> <span class="p">=</span> <span class="k">weak</span> <span class="k">global</span> <span class="k">i32</span> <span class="m">0</span>   <span class="c">; type of @H is i32*</span>
+
+<span class="k">define</span> <span class="k">i32</span> <span class="vg">@test</span><span class="p">(</span><span class="k">i1</span> <span class="nv">%Condition</span><span class="p">)</span> <span class="p">{</span>
+<span class="nl">entry:</span>
+  <span class="nv">%X</span> <span class="p">=</span> <span class="k">alloca</span> <span class="k">i32</span>           <span class="c">; type of %X is i32*.</span>
+  <span class="k">br</span> <span class="k">i1</span> <span class="nv">%Condition</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%cond_true</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%cond_false</span>
+
+<span class="nl">cond_true:</span>
+  <span class="nv">%X.0</span> <span class="p">=</span> <span class="k">load</span> <span class="k">i32</span><span class="p">*</span> <span class="vg">@G</span>
+  <span class="k">store</span> <span class="k">i32</span> <span class="nv">%X.0</span><span class="p">,</span> <span class="k">i32</span><span class="p">*</span> <span class="nv">%X</span>   <span class="c">; Update X</span>
+  <span class="k">br</span> <span class="kt">label</span> <span class="nv">%cond_next</span>
+
+<span class="nl">cond_false:</span>
+  <span class="nv">%X.1</span> <span class="p">=</span> <span class="k">load</span> <span class="k">i32</span><span class="p">*</span> <span class="vg">@H</span>
+  <span class="k">store</span> <span class="k">i32</span> <span class="nv">%X.1</span><span class="p">,</span> <span class="k">i32</span><span class="p">*</span> <span class="nv">%X</span>   <span class="c">; Update X</span>
+  <span class="k">br</span> <span class="kt">label</span> <span class="nv">%cond_next</span>
+
+<span class="nl">cond_next:</span>
+  <span class="nv">%X.2</span> <span class="p">=</span> <span class="k">load</span> <span class="k">i32</span><span class="p">*</span> <span class="nv">%X</span>       <span class="c">; Read X</span>
+  <span class="k">ret</span> <span class="k">i32</span> <span class="nv">%X.2</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>With this, we have discovered a way to handle arbitrary mutable
+variables without the need to create Phi nodes at all:</p>
+<ol class="arabic simple">
+<li>Each mutable variable becomes a stack allocation.</li>
+<li>Each read of the variable becomes a load from the stack.</li>
+<li>Each update of the variable becomes a store to the stack.</li>
+<li>Taking the address of a variable just uses the stack address
+directly.</li>
+</ol>
+<p>While this solution has solved our immediate problem, it introduced
+another one: we have now apparently introduced a lot of stack traffic
+for very simple and common operations, a major performance problem.
+Fortunately for us, the LLVM optimizer has a highly-tuned optimization
+pass named “mem2reg” that handles this case, promoting allocas like this
+into SSA registers, inserting Phi nodes as appropriate. If you run this
+example through the pass, for example, you’ll get:</p>
+<div class="highlight-bash"><div class="highlight"><pre><span class="nv">$ </span>llvm-as < example.ll | opt -mem2reg | llvm-dis
+ at G <span class="o">=</span> weak global i32 0
+ at H <span class="o">=</span> weak global i32 0
+
+define i32 @test<span class="o">(</span>i1 %Condition<span class="o">)</span> <span class="o">{</span>
+entry:
+  br i1 %Condition, label %cond_true, label %cond_false
+
+cond_true:
+  %X.0 <span class="o">=</span> load i32* @G
+  br label %cond_next
+
+cond_false:
+  %X.1 <span class="o">=</span> load i32* @H
+  br label %cond_next
+
+cond_next:
+  %X.01 <span class="o">=</span> phi i32 <span class="o">[</span> %X.1, %cond_false <span class="o">]</span>, <span class="o">[</span> %X.0, %cond_true <span class="o">]</span>
+  ret i32 %X.01
+<span class="o">}</span>
+</pre></div>
+</div>
+<p>The mem2reg pass implements the standard “iterated dominance frontier”
+algorithm for constructing SSA form and has a number of optimizations
+that speed up (very common) degenerate cases. The mem2reg optimization
+pass is the answer to dealing with mutable variables, and we highly
+recommend that you depend on it. Note that mem2reg only works on
+variables in certain circumstances:</p>
+<ol class="arabic simple">
+<li>mem2reg is alloca-driven: it looks for allocas and if it can handle
+them, it promotes them. It does not apply to global variables or heap
+allocations.</li>
+<li>mem2reg only looks for alloca instructions in the entry block of the
+function. Being in the entry block guarantees that the alloca is only
+executed once, which makes analysis simpler.</li>
+<li>mem2reg only promotes allocas whose uses are direct loads and stores.
+If the address of the stack object is passed to a function, or if any
+funny pointer arithmetic is involved, the alloca will not be
+promoted.</li>
+<li>mem2reg only works on allocas of <a class="reference external" href="../LangRef.html#t_classifications">first
+class</a> values (such as pointers,
+scalars and vectors), and only if the array size of the allocation is
+1 (or missing in the .ll file). mem2reg is not capable of promoting
+structs or arrays to registers. Note that the “scalarrepl” pass is
+more powerful and can promote structs, “unions”, and arrays in many
+cases.</li>
+</ol>
+<p>All of these properties are easy to satisfy for most imperative
+languages, and we’ll illustrate it below with Kaleidoscope. The final
+question you may be asking is: should I bother with this nonsense for my
+front-end? Wouldn’t it be better if I just did SSA construction
+directly, avoiding use of the mem2reg optimization pass? In short, we
+strongly recommend that you use this technique for building SSA form,
+unless there is an extremely good reason not to. Using this technique
+is:</p>
+<ul class="simple">
+<li>Proven and well tested: clang uses this technique
+for local mutable variables. As such, the most common clients of LLVM
+are using this to handle a bulk of their variables. You can be sure
+that bugs are found fast and fixed early.</li>
+<li>Extremely Fast: mem2reg has a number of special cases that make it
+fast in common cases as well as fully general. For example, it has
+fast-paths for variables that are only used in a single block,
+variables that only have one assignment point, good heuristics to
+avoid insertion of unneeded phi nodes, etc.</li>
+<li>Needed for debug info generation: <a class="reference external" href="../SourceLevelDebugging.html">Debug information in
+LLVM</a> relies on having the address of
+the variable exposed so that debug info can be attached to it. This
+technique dovetails very naturally with this style of debug info.</li>
+</ul>
+<p>If nothing else, this makes it much easier to get your front-end up and
+running, and is very simple to implement. Lets extend Kaleidoscope with
+mutable variables now!</p>
+</div>
+<div class="section" id="mutable-variables-in-kaleidoscope">
+<h2><a class="toc-backref" href="#id5">7.4. Mutable Variables in Kaleidoscope</a><a class="headerlink" href="#mutable-variables-in-kaleidoscope" title="Permalink to this headline">¶</a></h2>
+<p>Now that we know the sort of problem we want to tackle, lets see what
+this looks like in the context of our little Kaleidoscope language.
+We’re going to add two features:</p>
+<ol class="arabic simple">
+<li>The ability to mutate variables with the ‘=’ operator.</li>
+<li>The ability to define new variables.</li>
+</ol>
+<p>While the first item is really what this is about, we only have
+variables for incoming arguments as well as for induction variables, and
+redefining those only goes so far :). Also, the ability to define new
+variables is a useful thing regardless of whether you will be mutating
+them. Here’s a motivating example that shows how we could use these:</p>
+<div class="highlight-python"><div class="highlight"><pre># Define ':' for sequencing: as a low-precedence operator that ignores operands
+# and just returns the RHS.
+def binary : 1 (x y) y;
+
+# Recursive fib, we could do this before.
+def fib(x)
+  if (x < 3) then
+    1
+  else
+    fib(x-1)+fib(x-2);
+
+# Iterative fib.
+def fibi(x)
+  var a = 1, b = 1, c in
+  (for i = 3, i < x in
+     c = a + b :
+     a = b :
+     b = c) :
+  b;
+
+# Call it.
+fibi(10);
+</pre></div>
+</div>
+<p>In order to mutate variables, we have to change our existing variables
+to use the “alloca trick”. Once we have that, we’ll add our new
+operator, then extend Kaleidoscope to support new variable definitions.</p>
+</div>
+<div class="section" id="adjusting-existing-variables-for-mutation">
+<h2><a class="toc-backref" href="#id6">7.5. Adjusting Existing Variables for Mutation</a><a class="headerlink" href="#adjusting-existing-variables-for-mutation" title="Permalink to this headline">¶</a></h2>
+<p>The symbol table in Kaleidoscope is managed at code generation time by
+the ‘<tt class="docutils literal"><span class="pre">NamedValues</span></tt>‘ map. This map currently keeps track of the LLVM
+“Value*” that holds the double value for the named variable. In order
+to support mutation, we need to change this slightly, so that it
+<tt class="docutils literal"><span class="pre">NamedValues</span></tt> holds the <em>memory location</em> of the variable in question.
+Note that this change is a refactoring: it changes the structure of the
+code, but does not (by itself) change the behavior of the compiler. All
+of these changes are isolated in the Kaleidoscope code generator.</p>
+<p>At this point in Kaleidoscope’s development, it only supports variables
+for two things: incoming arguments to functions and the induction
+variable of ‘for’ loops. For consistency, we’ll allow mutation of these
+variables in addition to other user-defined variables. This means that
+these will both need memory locations.</p>
+<p>To start our transformation of Kaleidoscope, we’ll change the
+NamedValues map so that it maps to AllocaInst* instead of Value*. Once
+we do this, the C++ compiler will tell us what parts of the code we need
+to update:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">AllocaInst</span><span class="o">*></span> <span class="n">NamedValues</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>Also, since we will need to create these alloca’s, we’ll use a helper
+function that ensures that the allocas are created in the entry block of
+the function:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of</span>
+<span class="c1">/// the function.  This is used for mutable variables etc.</span>
+<span class="k">static</span> <span class="n">AllocaInst</span> <span class="o">*</span><span class="nf">CreateEntryBlockAlloca</span><span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span><span class="p">,</span>
+                                          <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">VarName</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">IRBuilder</span><span class="o"><></span> <span class="n">TmpB</span><span class="p">(</span><span class="o">&</span><span class="n">TheFunction</span><span class="o">-></span><span class="n">getEntryBlock</span><span class="p">(),</span>
+                 <span class="n">TheFunction</span><span class="o">-></span><span class="n">getEntryBlock</span><span class="p">().</span><span class="n">begin</span><span class="p">());</span>
+  <span class="k">return</span> <span class="n">TmpB</span><span class="p">.</span><span class="n">CreateAlloca</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="mi">0</span><span class="p">,</span>
+                           <span class="n">VarName</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>This funny looking code creates an IRBuilder object that is pointing at
+the first instruction (.begin()) of the entry block. It then creates an
+alloca with the expected name and returns it. Because all values in
+Kaleidoscope are doubles, there is no need to pass in a type to use.</p>
+<p>With this in place, the first functionality change we want to make is to
+variable references. In our new scheme, variables live on the stack, so
+code generating a reference to them actually needs to produce a load
+from the stack slot:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">Value</span> <span class="o">*</span><span class="n">VariableExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Look this variable up in the function.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">V</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">Name</span><span class="p">];</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">V</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown variable name"</span><span class="p">);</span>
+
+  <span class="c1">// Load the value.</span>
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateLoad</span><span class="p">(</span><span class="n">V</span><span class="p">,</span> <span class="n">Name</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>As you can see, this is pretty straightforward. Now we need to update
+the things that define the variables to set up the alloca. We’ll start
+with <tt class="docutils literal"><span class="pre">ForExprAST::Codegen</span></tt> (see the <a class="reference external" href="#code">full code listing</a> for
+the unabridged code):</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+
+<span class="c1">// Create an alloca for the variable in the entry block.</span>
+<span class="n">AllocaInst</span> <span class="o">*</span><span class="n">Alloca</span> <span class="o">=</span> <span class="n">CreateEntryBlockAlloca</span><span class="p">(</span><span class="n">TheFunction</span><span class="p">,</span> <span class="n">VarName</span><span class="p">);</span>
+
+  <span class="c1">// Emit the start code first, without 'variable' in scope.</span>
+<span class="n">Value</span> <span class="o">*</span><span class="n">StartVal</span> <span class="o">=</span> <span class="n">Start</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">StartVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+<span class="c1">// Store the value into the alloca.</span>
+<span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">StartVal</span><span class="p">,</span> <span class="n">Alloca</span><span class="p">);</span>
+<span class="p">...</span>
+
+<span class="c1">// Compute the end condition.</span>
+<span class="n">Value</span> <span class="o">*</span><span class="n">EndCond</span> <span class="o">=</span> <span class="n">End</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">EndCond</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="n">EndCond</span><span class="p">;</span>
+
+<span class="c1">// Reload, increment, and restore the alloca.  This handles the case where</span>
+<span class="c1">// the body of the loop mutates the variable.</span>
+<span class="n">Value</span> <span class="o">*</span><span class="n">CurVar</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateLoad</span><span class="p">(</span><span class="n">Alloca</span><span class="p">);</span>
+<span class="n">Value</span> <span class="o">*</span><span class="n">NextVar</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFAdd</span><span class="p">(</span><span class="n">CurVar</span><span class="p">,</span> <span class="n">StepVal</span><span class="p">,</span> <span class="s">"nextvar"</span><span class="p">);</span>
+<span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">NextVar</span><span class="p">,</span> <span class="n">Alloca</span><span class="p">);</span>
+<span class="p">...</span>
+</pre></div>
+</div>
+<p>This code is virtually identical to the code <a class="reference external" href="LangImpl5.html#forcodegen">before we allowed mutable
+variables</a>. The big difference is that we
+no longer have to construct a PHI node, and we use load/store to access
+the variable as needed.</p>
+<p>To support mutable argument variables, we need to also make allocas for
+them. The code for this is also pretty simple:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// CreateArgumentAllocas - Create an alloca for each argument and register the</span>
+<span class="c1">/// argument in the symbol table so that references to it will succeed.</span>
+<span class="kt">void</span> <span class="n">PrototypeAST</span><span class="o">::</span><span class="n">CreateArgumentAllocas</span><span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">F</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Function</span><span class="o">::</span><span class="n">arg_iterator</span> <span class="n">AI</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">arg_begin</span><span class="p">();</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">Idx</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">Idx</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">Idx</span><span class="p">,</span> <span class="o">++</span><span class="n">AI</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Create an alloca for this variable.</span>
+    <span class="n">AllocaInst</span> <span class="o">*</span><span class="n">Alloca</span> <span class="o">=</span> <span class="n">CreateEntryBlockAlloca</span><span class="p">(</span><span class="n">F</span><span class="p">,</span> <span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]);</span>
+
+    <span class="c1">// Store the initial value into the alloca.</span>
+    <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">AI</span><span class="p">,</span> <span class="n">Alloca</span><span class="p">);</span>
+
+    <span class="c1">// Add arguments to variable symbol table.</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]]</span> <span class="o">=</span> <span class="n">Alloca</span><span class="p">;</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>For each argument, we make an alloca, store the input value to the
+function into the alloca, and register the alloca as the memory location
+for the argument. This method gets invoked by <tt class="docutils literal"><span class="pre">FunctionAST::Codegen</span></tt>
+right after it sets up the entry block for the function.</p>
+<p>The final missing piece is adding the mem2reg pass, which allows us to
+get good codegen once again:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Set up the optimizer pipeline.  Start with registering info about how the</span>
+<span class="c1">// target lays out data structures.</span>
+<span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="k">new</span> <span class="n">DataLayout</span><span class="p">(</span><span class="o">*</span><span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">getDataLayout</span><span class="p">()));</span>
+<span class="c1">// Promote allocas to registers.</span>
+<span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createPromoteMemoryToRegisterPass</span><span class="p">());</span>
+<span class="c1">// Do simple "peephole" optimizations and bit-twiddling optzns.</span>
+<span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createInstructionCombiningPass</span><span class="p">());</span>
+<span class="c1">// Reassociate expressions.</span>
+<span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createReassociatePass</span><span class="p">());</span>
+</pre></div>
+</div>
+<p>It is interesting to see what the code looks like before and after the
+mem2reg optimization runs. For example, this is the before/after code
+for our recursive fib function. Before the optimization:</p>
+<div class="highlight-llvm"><div class="highlight"><pre><span class="k">define</span> <span class="kt">double</span> <span class="vg">@fib</span><span class="p">(</span><span class="kt">double</span> <span class="nv">%x</span><span class="p">)</span> <span class="p">{</span>
+<span class="nl">entry:</span>
+  <span class="nv">%x1</span> <span class="p">=</span> <span class="k">alloca</span> <span class="kt">double</span>
+  <span class="k">store</span> <span class="kt">double</span> <span class="nv">%x</span><span class="p">,</span> <span class="kt">double</span><span class="p">*</span> <span class="nv">%x1</span>
+  <span class="nv">%x2</span> <span class="p">=</span> <span class="k">load</span> <span class="kt">double</span><span class="p">*</span> <span class="nv">%x1</span>
+  <span class="nv">%cmptmp</span> <span class="p">=</span> <span class="k">fcmp</span> <span class="k">ult</span> <span class="kt">double</span> <span class="nv">%x2</span><span class="p">,</span> <span class="m">3.000000e+00</span>
+  <span class="nv">%booltmp</span> <span class="p">=</span> <span class="k">uitofp</span> <span class="k">i1</span> <span class="nv">%cmptmp</span> <span class="k">to</span> <span class="kt">double</span>
+  <span class="nv">%ifcond</span> <span class="p">=</span> <span class="k">fcmp</span> <span class="k">one</span> <span class="kt">double</span> <span class="nv">%booltmp</span><span class="p">,</span> <span class="m">0.000000e+00</span>
+  <span class="k">br</span> <span class="k">i1</span> <span class="nv">%ifcond</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%then</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%else</span>
+
+<span class="nl">then:</span>       <span class="c">; preds = %entry</span>
+  <span class="k">br</span> <span class="kt">label</span> <span class="nv">%ifcont</span>
+
+<span class="nl">else:</span>       <span class="c">; preds = %entry</span>
+  <span class="nv">%x3</span> <span class="p">=</span> <span class="k">load</span> <span class="kt">double</span><span class="p">*</span> <span class="nv">%x1</span>
+  <span class="nv">%subtmp</span> <span class="p">=</span> <span class="k">fsub</span> <span class="kt">double</span> <span class="nv">%x3</span><span class="p">,</span> <span class="m">1.000000e+00</span>
+  <span class="nv">%calltmp</span> <span class="p">=</span> <span class="k">call</span> <span class="kt">double</span> <span class="vg">@fib</span><span class="p">(</span><span class="kt">double</span> <span class="nv">%subtmp</span><span class="p">)</span>
+  <span class="nv">%x4</span> <span class="p">=</span> <span class="k">load</span> <span class="kt">double</span><span class="p">*</span> <span class="nv">%x1</span>
+  <span class="nv">%subtmp5</span> <span class="p">=</span> <span class="k">fsub</span> <span class="kt">double</span> <span class="nv">%x4</span><span class="p">,</span> <span class="m">2.000000e+00</span>
+  <span class="nv">%calltmp6</span> <span class="p">=</span> <span class="k">call</span> <span class="kt">double</span> <span class="vg">@fib</span><span class="p">(</span><span class="kt">double</span> <span class="nv">%subtmp5</span><span class="p">)</span>
+  <span class="nv">%addtmp</span> <span class="p">=</span> <span class="k">fadd</span> <span class="kt">double</span> <span class="nv">%calltmp</span><span class="p">,</span> <span class="nv">%calltmp6</span>
+  <span class="k">br</span> <span class="kt">label</span> <span class="nv">%ifcont</span>
+
+<span class="nl">ifcont:</span>     <span class="c">; preds = %else, %then</span>
+  <span class="nv">%iftmp</span> <span class="p">=</span> <span class="k">phi</span> <span class="kt">double</span> <span class="p">[</span> <span class="m">1.000000e+00</span><span class="p">,</span> <span class="nv">%then</span> <span class="p">],</span> <span class="p">[</span> <span class="nv">%addtmp</span><span class="p">,</span> <span class="nv">%else</span> <span class="p">]</span>
+  <span class="k">ret</span> <span class="kt">double</span> <span class="nv">%iftmp</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Here there is only one variable (x, the input argument) but you can
+still see the extremely simple-minded code generation strategy we are
+using. In the entry block, an alloca is created, and the initial input
+value is stored into it. Each reference to the variable does a reload
+from the stack. Also, note that we didn’t modify the if/then/else
+expression, so it still inserts a PHI node. While we could make an
+alloca for it, it is actually easier to create a PHI node for it, so we
+still just make the PHI.</p>
+<p>Here is the code after the mem2reg pass runs:</p>
+<div class="highlight-llvm"><div class="highlight"><pre><span class="k">define</span> <span class="kt">double</span> <span class="vg">@fib</span><span class="p">(</span><span class="kt">double</span> <span class="nv">%x</span><span class="p">)</span> <span class="p">{</span>
+<span class="nl">entry:</span>
+  <span class="nv">%cmptmp</span> <span class="p">=</span> <span class="k">fcmp</span> <span class="k">ult</span> <span class="kt">double</span> <span class="nv">%x</span><span class="p">,</span> <span class="m">3.000000e+00</span>
+  <span class="nv">%booltmp</span> <span class="p">=</span> <span class="k">uitofp</span> <span class="k">i1</span> <span class="nv">%cmptmp</span> <span class="k">to</span> <span class="kt">double</span>
+  <span class="nv">%ifcond</span> <span class="p">=</span> <span class="k">fcmp</span> <span class="k">one</span> <span class="kt">double</span> <span class="nv">%booltmp</span><span class="p">,</span> <span class="m">0.000000e+00</span>
+  <span class="k">br</span> <span class="k">i1</span> <span class="nv">%ifcond</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%then</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%else</span>
+
+<span class="nl">then:</span>
+  <span class="k">br</span> <span class="kt">label</span> <span class="nv">%ifcont</span>
+
+<span class="nl">else:</span>
+  <span class="nv">%subtmp</span> <span class="p">=</span> <span class="k">fsub</span> <span class="kt">double</span> <span class="nv">%x</span><span class="p">,</span> <span class="m">1.000000e+00</span>
+  <span class="nv">%calltmp</span> <span class="p">=</span> <span class="k">call</span> <span class="kt">double</span> <span class="vg">@fib</span><span class="p">(</span><span class="kt">double</span> <span class="nv">%subtmp</span><span class="p">)</span>
+  <span class="nv">%subtmp5</span> <span class="p">=</span> <span class="k">fsub</span> <span class="kt">double</span> <span class="nv">%x</span><span class="p">,</span> <span class="m">2.000000e+00</span>
+  <span class="nv">%calltmp6</span> <span class="p">=</span> <span class="k">call</span> <span class="kt">double</span> <span class="vg">@fib</span><span class="p">(</span><span class="kt">double</span> <span class="nv">%subtmp5</span><span class="p">)</span>
+  <span class="nv">%addtmp</span> <span class="p">=</span> <span class="k">fadd</span> <span class="kt">double</span> <span class="nv">%calltmp</span><span class="p">,</span> <span class="nv">%calltmp6</span>
+  <span class="k">br</span> <span class="kt">label</span> <span class="nv">%ifcont</span>
+
+<span class="nl">ifcont:</span>     <span class="c">; preds = %else, %then</span>
+  <span class="nv">%iftmp</span> <span class="p">=</span> <span class="k">phi</span> <span class="kt">double</span> <span class="p">[</span> <span class="m">1.000000e+00</span><span class="p">,</span> <span class="nv">%then</span> <span class="p">],</span> <span class="p">[</span> <span class="nv">%addtmp</span><span class="p">,</span> <span class="nv">%else</span> <span class="p">]</span>
+  <span class="k">ret</span> <span class="kt">double</span> <span class="nv">%iftmp</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>This is a trivial case for mem2reg, since there are no redefinitions of
+the variable. The point of showing this is to calm your tension about
+inserting such blatent inefficiencies :).</p>
+<p>After the rest of the optimizers run, we get:</p>
+<div class="highlight-llvm"><div class="highlight"><pre><span class="k">define</span> <span class="kt">double</span> <span class="vg">@fib</span><span class="p">(</span><span class="kt">double</span> <span class="nv">%x</span><span class="p">)</span> <span class="p">{</span>
+<span class="nl">entry:</span>
+  <span class="nv">%cmptmp</span> <span class="p">=</span> <span class="k">fcmp</span> <span class="k">ult</span> <span class="kt">double</span> <span class="nv">%x</span><span class="p">,</span> <span class="m">3.000000e+00</span>
+  <span class="nv">%booltmp</span> <span class="p">=</span> <span class="k">uitofp</span> <span class="k">i1</span> <span class="nv">%cmptmp</span> <span class="k">to</span> <span class="kt">double</span>
+  <span class="nv">%ifcond</span> <span class="p">=</span> <span class="k">fcmp</span> <span class="k">ueq</span> <span class="kt">double</span> <span class="nv">%booltmp</span><span class="p">,</span> <span class="m">0.000000e+00</span>
+  <span class="k">br</span> <span class="k">i1</span> <span class="nv">%ifcond</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%else</span><span class="p">,</span> <span class="kt">label</span> <span class="nv">%ifcont</span>
+
+<span class="nl">else:</span>
+  <span class="nv">%subtmp</span> <span class="p">=</span> <span class="k">fsub</span> <span class="kt">double</span> <span class="nv">%x</span><span class="p">,</span> <span class="m">1.000000e+00</span>
+  <span class="nv">%calltmp</span> <span class="p">=</span> <span class="k">call</span> <span class="kt">double</span> <span class="vg">@fib</span><span class="p">(</span><span class="kt">double</span> <span class="nv">%subtmp</span><span class="p">)</span>
+  <span class="nv">%subtmp5</span> <span class="p">=</span> <span class="k">fsub</span> <span class="kt">double</span> <span class="nv">%x</span><span class="p">,</span> <span class="m">2.000000e+00</span>
+  <span class="nv">%calltmp6</span> <span class="p">=</span> <span class="k">call</span> <span class="kt">double</span> <span class="vg">@fib</span><span class="p">(</span><span class="kt">double</span> <span class="nv">%subtmp5</span><span class="p">)</span>
+  <span class="nv">%addtmp</span> <span class="p">=</span> <span class="k">fadd</span> <span class="kt">double</span> <span class="nv">%calltmp</span><span class="p">,</span> <span class="nv">%calltmp6</span>
+  <span class="k">ret</span> <span class="kt">double</span> <span class="nv">%addtmp</span>
+
+<span class="nl">ifcont:</span>
+  <span class="k">ret</span> <span class="kt">double</span> <span class="m">1.000000e+00</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Here we see that the simplifycfg pass decided to clone the return
+instruction into the end of the ‘else’ block. This allowed it to
+eliminate some branches and the PHI node.</p>
+<p>Now that all symbol table references are updated to use stack variables,
+we’ll add the assignment operator.</p>
+</div>
+<div class="section" id="new-assignment-operator">
+<h2><a class="toc-backref" href="#id7">7.6. New Assignment Operator</a><a class="headerlink" href="#new-assignment-operator" title="Permalink to this headline">¶</a></h2>
+<p>With our current framework, adding a new assignment operator is really
+simple. We will parse it just like any other binary operator, but handle
+it internally (instead of allowing the user to define it). The first
+step is to set a precedence:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">int</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Install standard binary operators.</span>
+  <span class="c1">// 1 is lowest precedence.</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'='</span><span class="p">]</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'<'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'+'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'-'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>Now that the parser knows the precedence of the binary operator, it
+takes care of all the parsing and AST generation. We just need to
+implement codegen for the assignment operator. This looks like:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">Value</span> <span class="o">*</span><span class="n">BinaryExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Special case '=' because we don't want to emit the LHS as an expression.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Op</span> <span class="o">==</span> <span class="sc">'='</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Assignment requires the LHS to be an identifier.</span>
+    <span class="n">VariableExprAST</span> <span class="o">*</span><span class="n">LHSE</span> <span class="o">=</span> <span class="k">dynamic_cast</span><span class="o"><</span><span class="n">VariableExprAST</span><span class="o">*></span><span class="p">(</span><span class="n">LHS</span><span class="p">);</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">LHSE</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"destination of '=' must be a variable"</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>Unlike the rest of the binary operators, our assignment operator doesn’t
+follow the “emit LHS, emit RHS, do computation” model. As such, it is
+handled as a special case before the other binary operators are handled.
+The other strange thing is that it requires the LHS to be a variable. It
+is invalid to have “(x+1) = expr” - only things like “x = expr” are
+allowed.</p>
+<div class="highlight-c++"><div class="highlight"><pre>  <span class="c1">// Codegen the RHS.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Val</span> <span class="o">=</span> <span class="n">RHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Val</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Look up the name.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Variable</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">LHSE</span><span class="o">-></span><span class="n">getName</span><span class="p">()];</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Variable</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown variable name"</span><span class="p">);</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">Val</span><span class="p">,</span> <span class="n">Variable</span><span class="p">);</span>
+  <span class="k">return</span> <span class="n">Val</span><span class="p">;</span>
+<span class="p">}</span>
+<span class="p">...</span>
+</pre></div>
+</div>
+<p>Once we have the variable, codegen’ing the assignment is
+straightforward: we emit the RHS of the assignment, create a store, and
+return the computed value. Returning a value allows for chained
+assignments like “X = (Y = Z)”.</p>
+<p>Now that we have an assignment operator, we can mutate loop variables
+and arguments. For example, we can now run code like this:</p>
+<div class="highlight-python"><div class="highlight"><pre># Function to print a double.
+extern printd(x);
+
+# Define ':' for sequencing: as a low-precedence operator that ignores operands
+# and just returns the RHS.
+def binary : 1 (x y) y;
+
+def test(x)
+  printd(x) :
+  x = 4 :
+  printd(x);
+
+test(123);
+</pre></div>
+</div>
+<p>When run, this example prints “123” and then “4”, showing that we did
+actually mutate the value! Okay, we have now officially implemented our
+goal: getting this to work requires SSA construction in the general
+case. However, to be really useful, we want the ability to define our
+own local variables, lets add this next!</p>
+</div>
+<div class="section" id="user-defined-local-variables">
+<h2><a class="toc-backref" href="#id8">7.7. User-defined Local Variables</a><a class="headerlink" href="#user-defined-local-variables" title="Permalink to this headline">¶</a></h2>
+<p>Adding var/in is just like any other extension we made to
+Kaleidoscope: we extend the lexer, the parser, the AST and the code
+generator. The first step for adding our new ‘var/in’ construct is to
+extend the lexer. As before, this is pretty trivial, the code looks like
+this:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">enum</span> <span class="n">Token</span> <span class="p">{</span>
+  <span class="p">...</span>
+  <span class="c1">// var definition</span>
+  <span class="n">tok_var</span> <span class="o">=</span> <span class="o">-</span><span class="mi">13</span>
+<span class="p">...</span>
+<span class="p">}</span>
+<span class="p">...</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="n">gettok</span><span class="p">()</span> <span class="p">{</span>
+<span class="p">...</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"in"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_in</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"binary"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_binary</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"unary"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_unary</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"var"</span><span class="p">)</span> <span class="k">return</span> <span class="n">tok_var</span><span class="p">;</span>
+    <span class="k">return</span> <span class="n">tok_identifier</span><span class="p">;</span>
+<span class="p">...</span>
+</pre></div>
+</div>
+<p>The next step is to define the AST node that we will construct. For
+var/in, it looks like this:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// VarExprAST - Expression class for var/in</span>
+<span class="k">class</span> <span class="nc">VarExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">pair</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">ExprAST</span><span class="o">*></span> <span class="o">></span> <span class="n">VarNames</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+<span class="nl">public:</span>
+  <span class="n">VarExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">pair</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">ExprAST</span><span class="o">*></span> <span class="o">></span> <span class="o">&</span><span class="n">varnames</span><span class="p">,</span>
+             <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span>
+  <span class="o">:</span> <span class="n">VarNames</span><span class="p">(</span><span class="n">varnames</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="k">virtual</span> <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+</pre></div>
+</div>
+<p>var/in allows a list of names to be defined all at once, and each name
+can optionally have an initializer value. As such, we capture this
+information in the VarNames vector. Also, var/in has a body, this body
+is allowed to access the variables defined by the var/in.</p>
+<p>With this in place, we can define the parser pieces. The first thing we
+do is add it as a primary expression:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// primary</span>
+<span class="c1">///   ::= identifierexpr</span>
+<span class="c1">///   ::= numberexpr</span>
+<span class="c1">///   ::= parenexpr</span>
+<span class="c1">///   ::= ifexpr</span>
+<span class="c1">///   ::= forexpr</span>
+<span class="c1">///   ::= varexpr</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParsePrimary</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="nl">default:</span> <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"unknown token when expecting an expression"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>: <span class="k">return</span> <span class="n">ParseIdentifierExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_number</span>:     <span class="k">return</span> <span class="n">ParseNumberExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="sc">'('</span>:            <span class="k">return</span> <span class="n">ParseParenExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_if</span>:         <span class="k">return</span> <span class="n">ParseIfExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_for</span>:        <span class="k">return</span> <span class="n">ParseForExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_var</span>:        <span class="k">return</span> <span class="n">ParseVarExpr</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Next we define ParseVarExpr:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">/// varexpr ::= 'var' identifier ('=' expression)?</span>
+<span class="c1">//                    (',' identifier ('=' expression)?)* 'in' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseVarExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span>  <span class="c1">// eat the var.</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">pair</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">ExprAST</span><span class="o">*></span> <span class="o">></span> <span class="n">VarNames</span><span class="p">;</span>
+
+  <span class="c1">// At least one variable name is required.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected identifier after var"</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>The first part of this code parses the list of identifier/expr pairs
+into the local <tt class="docutils literal"><span class="pre">VarNames</span></tt> vector.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span>  <span class="c1">// eat identifier.</span>
+
+  <span class="c1">// Read the optional initializer.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Init</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">'='</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the '='.</span>
+
+    <span class="n">Init</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Init</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="n">VarNames</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">make_pair</span><span class="p">(</span><span class="n">Name</span><span class="p">,</span> <span class="n">Init</span><span class="p">));</span>
+
+  <span class="c1">// End of var list, exit loop.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span> <span class="k">break</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the ','.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected identifier list after var"</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Once all the variables are parsed, we then parse the body and create the
+AST node:</p>
+<div class="highlight-c++"><div class="highlight"><pre>  <span class="c1">// At this point, we have to have 'in'.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_in</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected 'in' keyword after 'var'"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>  <span class="c1">// eat 'in'.</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Body</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="nf">VarExprAST</span><span class="p">(</span><span class="n">VarNames</span><span class="p">,</span> <span class="n">Body</span><span class="p">);</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>Now that we can parse and represent the code, we need to support
+emission of LLVM IR for it. This code starts out with:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">Value</span> <span class="o">*</span><span class="n">VarExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">AllocaInst</span> <span class="o">*></span> <span class="n">OldBindings</span><span class="p">;</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+
+  <span class="c1">// Register all variables and emit their initializer.</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">VarNames</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">VarName</span> <span class="o">=</span> <span class="n">VarNames</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">first</span><span class="p">;</span>
+    <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Init</span> <span class="o">=</span> <span class="n">VarNames</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">second</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>Basically it loops over all the variables, installing them one at a
+time. For each variable we put into the symbol table, we remember the
+previous value that we replace in OldBindings.</p>
+<div class="highlight-c++"><div class="highlight"><pre>  <span class="c1">// Emit the initializer before adding the variable to scope, this prevents</span>
+  <span class="c1">// the initializer from referencing the variable itself, and permits stuff</span>
+  <span class="c1">// like this:</span>
+  <span class="c1">//  var a = 1 in</span>
+  <span class="c1">//    var a = a in ...   # refers to outer 'a'.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">InitVal</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Init</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">InitVal</span> <span class="o">=</span> <span class="n">Init</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">InitVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span> <span class="c1">// If not specified, use 0.0.</span>
+    <span class="n">InitVal</span> <span class="o">=</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">));</span>
+  <span class="p">}</span>
+
+  <span class="n">AllocaInst</span> <span class="o">*</span><span class="n">Alloca</span> <span class="o">=</span> <span class="n">CreateEntryBlockAlloca</span><span class="p">(</span><span class="n">TheFunction</span><span class="p">,</span> <span class="n">VarName</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">InitVal</span><span class="p">,</span> <span class="n">Alloca</span><span class="p">);</span>
+
+  <span class="c1">// Remember the old variable binding so that we can restore the binding when</span>
+  <span class="c1">// we unrecurse.</span>
+  <span class="n">OldBindings</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]);</span>
+
+  <span class="c1">// Remember this binding.</span>
+  <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">Alloca</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>There are more comments here than code. The basic idea is that we emit
+the initializer, create the alloca, then update the symbol table to
+point to it. Once all the variables are installed in the symbol table,
+we evaluate the body of the var/in expression:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Codegen the body, now that all vars are in scope.</span>
+<span class="n">Value</span> <span class="o">*</span><span class="n">BodyVal</span> <span class="o">=</span> <span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+<span class="k">if</span> <span class="p">(</span><span class="n">BodyVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>Finally, before returning, we restore the previous variable bindings:</p>
+<div class="highlight-c++"><div class="highlight"><pre>  <span class="c1">// Pop all our variables from scope.</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">VarNames</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarNames</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">first</span><span class="p">]</span> <span class="o">=</span> <span class="n">OldBindings</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
+
+  <span class="c1">// Return the body computation.</span>
+  <span class="k">return</span> <span class="n">BodyVal</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>The end result of all of this is that we get properly scoped variable
+definitions, and we even (trivially) allow mutation of them :).</p>
+<p>With this, we completed what we set out to do. Our nice iterative fib
+example from the intro compiles and runs just fine. The mem2reg pass
+optimizes all of our stack variables into SSA registers, inserting PHI
+nodes where needed, and our front-end remains simple: no “iterated
+dominance frontier” computation anywhere in sight.</p>
+</div>
+<div class="section" id="id1">
+<h2><a class="toc-backref" href="#id9">7.8. Full Code Listing</a><a class="headerlink" href="#id1" title="Permalink to this headline">¶</a></h2>
+<p>Here is the complete code listing for our running example, enhanced with
+mutable variables and var/in support. To build this example, use:</p>
+<div class="highlight-bash"><div class="highlight"><pre><span class="c"># Compile</span>
+clang++ -g toy.cpp <span class="sb">`</span>llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native<span class="sb">`</span> -O3 -o toy
+<span class="c"># Run</span>
+./toy
+</pre></div>
+</div>
+<p>Here is the code:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include "llvm/ADT/STLExtras.h"</span>
+<span class="cp">#include "llvm/Analysis/Passes.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/ExecutionEngine.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/MCJIT.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/SectionMemoryManager.h"</span>
+<span class="cp">#include "llvm/IR/DataLayout.h"</span>
+<span class="cp">#include "llvm/IR/DerivedTypes.h"</span>
+<span class="cp">#include "llvm/IR/IRBuilder.h"</span>
+<span class="cp">#include "llvm/IR/LLVMContext.h"</span>
+<span class="cp">#include "llvm/IR/LegacyPassManager.h"</span>
+<span class="cp">#include "llvm/IR/Module.h"</span>
+<span class="cp">#include "llvm/IR/Verifier.h"</span>
+<span class="cp">#include "llvm/Support/TargetSelect.h"</span>
+<span class="cp">#include "llvm/Transforms/Scalar.h"</span>
+<span class="cp">#include <cctype></span>
+<span class="cp">#include <cstdio></span>
+<span class="cp">#include <map></span>
+<span class="cp">#include <string></span>
+<span class="cp">#include <vector></span>
+<span class="k">using</span> <span class="k">namespace</span> <span class="n">llvm</span><span class="p">;</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Lexer</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">// The lexer returns tokens [0-255] if it is an unknown character, otherwise one</span>
+<span class="c1">// of these for known things.</span>
+<span class="k">enum</span> <span class="n">Token</span> <span class="p">{</span>
+  <span class="n">tok_eof</span> <span class="o">=</span> <span class="o">-</span><span class="mi">1</span><span class="p">,</span>
+
+  <span class="c1">// commands</span>
+  <span class="n">tok_def</span> <span class="o">=</span> <span class="o">-</span><span class="mi">2</span><span class="p">,</span>
+  <span class="n">tok_extern</span> <span class="o">=</span> <span class="o">-</span><span class="mi">3</span><span class="p">,</span>
+
+  <span class="c1">// primary</span>
+  <span class="n">tok_identifier</span> <span class="o">=</span> <span class="o">-</span><span class="mi">4</span><span class="p">,</span>
+  <span class="n">tok_number</span> <span class="o">=</span> <span class="o">-</span><span class="mi">5</span><span class="p">,</span>
+
+  <span class="c1">// control</span>
+  <span class="n">tok_if</span> <span class="o">=</span> <span class="o">-</span><span class="mi">6</span><span class="p">,</span>
+  <span class="n">tok_then</span> <span class="o">=</span> <span class="o">-</span><span class="mi">7</span><span class="p">,</span>
+  <span class="n">tok_else</span> <span class="o">=</span> <span class="o">-</span><span class="mi">8</span><span class="p">,</span>
+  <span class="n">tok_for</span> <span class="o">=</span> <span class="o">-</span><span class="mi">9</span><span class="p">,</span>
+  <span class="n">tok_in</span> <span class="o">=</span> <span class="o">-</span><span class="mi">10</span><span class="p">,</span>
+
+  <span class="c1">// operators</span>
+  <span class="n">tok_binary</span> <span class="o">=</span> <span class="o">-</span><span class="mi">11</span><span class="p">,</span>
+  <span class="n">tok_unary</span> <span class="o">=</span> <span class="o">-</span><span class="mi">12</span><span class="p">,</span>
+
+  <span class="c1">// var definition</span>
+  <span class="n">tok_var</span> <span class="o">=</span> <span class="o">-</span><span class="mi">13</span>
+<span class="p">};</span>
+
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdentifierStr</span><span class="p">;</span> <span class="c1">// Filled in if tok_identifier</span>
+<span class="k">static</span> <span class="kt">double</span> <span class="n">NumVal</span><span class="p">;</span>             <span class="c1">// Filled in if tok_number</span>
+
+<span class="c1">/// gettok - Return the next token from standard input.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">gettok</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">static</span> <span class="kt">int</span> <span class="n">LastChar</span> <span class="o">=</span> <span class="sc">' '</span><span class="p">;</span>
+
+  <span class="c1">// Skip any whitespace.</span>
+  <span class="k">while</span> <span class="p">(</span><span class="n">isspace</span><span class="p">(</span><span class="n">LastChar</span><span class="p">))</span>
+    <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">isalpha</span><span class="p">(</span><span class="n">LastChar</span><span class="p">))</span> <span class="p">{</span> <span class="c1">// identifier: [a-zA-Z][a-zA-Z0-9]*</span>
+    <span class="n">IdentifierStr</span> <span class="o">=</span> <span class="n">LastChar</span><span class="p">;</span>
+    <span class="k">while</span> <span class="p">(</span><span class="n">isalnum</span><span class="p">((</span><span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">())))</span>
+      <span class="n">IdentifierStr</span> <span class="o">+=</span> <span class="n">LastChar</span><span class="p">;</span>
+
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"def"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_def</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"extern"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_extern</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"if"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_if</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"then"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_then</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"else"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_else</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"for"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_for</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"in"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_in</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"binary"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_binary</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"unary"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_unary</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"var"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_var</span><span class="p">;</span>
+    <span class="k">return</span> <span class="n">tok_identifier</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">isdigit</span><span class="p">(</span><span class="n">LastChar</span><span class="p">)</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">)</span> <span class="p">{</span> <span class="c1">// Number: [0-9.]+</span>
+    <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">NumStr</span><span class="p">;</span>
+    <span class="k">do</span> <span class="p">{</span>
+      <span class="n">NumStr</span> <span class="o">+=</span> <span class="n">LastChar</span><span class="p">;</span>
+      <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+    <span class="p">}</span> <span class="k">while</span> <span class="p">(</span><span class="n">isdigit</span><span class="p">(</span><span class="n">LastChar</span><span class="p">)</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">);</span>
+
+    <span class="n">NumVal</span> <span class="o">=</span> <span class="n">strtod</span><span class="p">(</span><span class="n">NumStr</span><span class="p">.</span><span class="n">c_str</span><span class="p">(),</span> <span class="mi">0</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">tok_number</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'#'</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Comment until end of line.</span>
+    <span class="k">do</span>
+      <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+    <span class="k">while</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">!=</span> <span class="n">EOF</span> <span class="o">&&</span> <span class="n">LastChar</span> <span class="o">!=</span> <span class="sc">'\n'</span> <span class="o">&&</span> <span class="n">LastChar</span> <span class="o">!=</span> <span class="sc">'\r'</span><span class="p">);</span>
+
+    <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">!=</span> <span class="n">EOF</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">gettok</span><span class="p">();</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Check for end of file.  Don't eat the EOF.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="n">EOF</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">tok_eof</span><span class="p">;</span>
+
+  <span class="c1">// Otherwise, just return the character as its ascii value.</span>
+  <span class="kt">int</span> <span class="n">ThisChar</span> <span class="o">=</span> <span class="n">LastChar</span><span class="p">;</span>
+  <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+  <span class="k">return</span> <span class="n">ThisChar</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Abstract Syntax Tree (aka Parse Tree)</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="k">namespace</span> <span class="p">{</span>
+<span class="c1">/// ExprAST - Base class for all expression nodes.</span>
+<span class="k">class</span> <span class="nc">ExprAST</span> <span class="p">{</span>
+<span class="nl">public:</span>
+  <span class="k">virtual</span> <span class="o">~</span><span class="n">ExprAST</span><span class="p">()</span> <span class="p">{}</span>
+  <span class="k">virtual</span> <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// NumberExprAST - Expression class for numeric literals like "1.0".</span>
+<span class="k">class</span> <span class="nc">NumberExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">double</span> <span class="n">Val</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">NumberExprAST</span><span class="p">(</span><span class="kt">double</span> <span class="n">val</span><span class="p">)</span> <span class="o">:</span> <span class="n">Val</span><span class="p">(</span><span class="n">val</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// VariableExprAST - Expression class for referencing a variable, like "a".</span>
+<span class="k">class</span> <span class="nc">VariableExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">VariableExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">name</span><span class="p">)</span> <span class="o">:</span> <span class="n">Name</span><span class="p">(</span><span class="n">name</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">getName</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">Name</span><span class="p">;</span> <span class="p">}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// UnaryExprAST - Expression class for a unary operator.</span>
+<span class="k">class</span> <span class="nc">UnaryExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">char</span> <span class="n">Opcode</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Operand</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">UnaryExprAST</span><span class="p">(</span><span class="kt">char</span> <span class="n">opcode</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">operand</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Opcode</span><span class="p">(</span><span class="n">opcode</span><span class="p">),</span> <span class="n">Operand</span><span class="p">(</span><span class="n">operand</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// BinaryExprAST - Expression class for a binary operator.</span>
+<span class="k">class</span> <span class="nc">BinaryExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">char</span> <span class="n">Op</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span><span class="p">,</span> <span class="o">*</span><span class="n">RHS</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">BinaryExprAST</span><span class="p">(</span><span class="kt">char</span> <span class="n">op</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">lhs</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">rhs</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Op</span><span class="p">(</span><span class="n">op</span><span class="p">),</span> <span class="n">LHS</span><span class="p">(</span><span class="n">lhs</span><span class="p">),</span> <span class="n">RHS</span><span class="p">(</span><span class="n">rhs</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// CallExprAST - Expression class for function calls.</span>
+<span class="k">class</span> <span class="nc">CallExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Callee</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="n">Args</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">CallExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">callee</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="o">&</span><span class="n">args</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Callee</span><span class="p">(</span><span class="n">callee</span><span class="p">),</span> <span class="n">Args</span><span class="p">(</span><span class="n">args</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// IfExprAST - Expression class for if/then/else.</span>
+<span class="k">class</span> <span class="nc">IfExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Cond</span><span class="p">,</span> <span class="o">*</span><span class="n">Then</span><span class="p">,</span> <span class="o">*</span><span class="n">Else</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">IfExprAST</span><span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">cond</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">then</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">_else</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Cond</span><span class="p">(</span><span class="n">cond</span><span class="p">),</span> <span class="n">Then</span><span class="p">(</span><span class="n">then</span><span class="p">),</span> <span class="n">Else</span><span class="p">(</span><span class="n">_else</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// ForExprAST - Expression class for for/in.</span>
+<span class="k">class</span> <span class="nc">ForExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">VarName</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Start</span><span class="p">,</span> <span class="o">*</span><span class="n">End</span><span class="p">,</span> <span class="o">*</span><span class="n">Step</span><span class="p">,</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">ForExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">varname</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">start</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">end</span><span class="p">,</span>
+             <span class="n">ExprAST</span> <span class="o">*</span><span class="n">step</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">VarName</span><span class="p">(</span><span class="n">varname</span><span class="p">),</span> <span class="n">Start</span><span class="p">(</span><span class="n">start</span><span class="p">),</span> <span class="n">End</span><span class="p">(</span><span class="n">end</span><span class="p">),</span> <span class="n">Step</span><span class="p">(</span><span class="n">step</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// VarExprAST - Expression class for var/in</span>
+<span class="k">class</span> <span class="nc">VarExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">pair</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*></span> <span class="o">></span> <span class="n">VarNames</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">VarExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">pair</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*></span> <span class="o">></span> <span class="o">&</span><span class="n">varnames</span><span class="p">,</span>
+             <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">VarNames</span><span class="p">(</span><span class="n">varnames</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// PrototypeAST - This class represents the "prototype" for a function,</span>
+<span class="c1">/// which captures its argument names as well as if it is an operator.</span>
+<span class="k">class</span> <span class="nc">PrototypeAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">Args</span><span class="p">;</span>
+  <span class="kt">bool</span> <span class="n">isOperator</span><span class="p">;</span>
+  <span class="kt">unsigned</span> <span class="n">Precedence</span><span class="p">;</span> <span class="c1">// Precedence if a binary op.</span>
+<span class="nl">public:</span>
+  <span class="n">PrototypeAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">name</span><span class="p">,</span> <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="o">&</span><span class="n">args</span><span class="p">,</span>
+               <span class="kt">bool</span> <span class="n">isoperator</span> <span class="o">=</span> <span class="nb">false</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">prec</span> <span class="o">=</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Name</span><span class="p">(</span><span class="n">name</span><span class="p">),</span> <span class="n">Args</span><span class="p">(</span><span class="n">args</span><span class="p">),</span> <span class="n">isOperator</span><span class="p">(</span><span class="n">isoperator</span><span class="p">),</span> <span class="n">Precedence</span><span class="p">(</span><span class="n">prec</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="kt">bool</span> <span class="n">isUnaryOp</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">isOperator</span> <span class="o">&&</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">==</span> <span class="mi">1</span><span class="p">;</span> <span class="p">}</span>
+  <span class="kt">bool</span> <span class="n">isBinaryOp</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">isOperator</span> <span class="o">&&</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">==</span> <span class="mi">2</span><span class="p">;</span> <span class="p">}</span>
+
+  <span class="kt">char</span> <span class="n">getOperatorName</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span>
+    <span class="n">assert</span><span class="p">(</span><span class="n">isUnaryOp</span><span class="p">()</span> <span class="o">||</span> <span class="n">isBinaryOp</span><span class="p">());</span>
+    <span class="k">return</span> <span class="n">Name</span><span class="p">[</span><span class="n">Name</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">-</span> <span class="mi">1</span><span class="p">];</span>
+  <span class="p">}</span>
+
+  <span class="kt">unsigned</span> <span class="n">getBinaryPrecedence</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">Precedence</span><span class="p">;</span> <span class="p">}</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+
+  <span class="kt">void</span> <span class="nf">CreateArgumentAllocas</span><span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">F</span><span class="p">);</span>
+<span class="p">};</span>
+
+<span class="c1">/// FunctionAST - This class represents a function definition itself.</span>
+<span class="k">class</span> <span class="nc">FunctionAST</span> <span class="p">{</span>
+  <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">FunctionAST</span><span class="p">(</span><span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">proto</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span> <span class="o">:</span> <span class="n">Proto</span><span class="p">(</span><span class="n">proto</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+<span class="p">}</span> <span class="c1">// end anonymous namespace</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Parser</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">/// CurTok/getNextToken - Provide a simple token buffer.  CurTok is the current</span>
+<span class="c1">/// token the parser is looking at.  getNextToken reads another token from the</span>
+<span class="c1">/// lexer and updates CurTok with its results.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="n">CurTok</span><span class="p">;</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">getNextToken</span><span class="p">()</span> <span class="p">{</span> <span class="k">return</span> <span class="n">CurTok</span> <span class="o">=</span> <span class="n">gettok</span><span class="p">();</span> <span class="p">}</span>
+
+<span class="c1">/// BinopPrecedence - This holds the precedence for each binary operator that is</span>
+<span class="c1">/// defined.</span>
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="kt">char</span><span class="p">,</span> <span class="kt">int</span><span class="o">></span> <span class="n">BinopPrecedence</span><span class="p">;</span>
+
+<span class="c1">/// GetTokPrecedence - Get the precedence of the pending binary operator token.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">GetTokPrecedence</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+    <span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
+
+  <span class="c1">// Make sure it's a declared binop.</span>
+  <span class="kt">int</span> <span class="n">TokPrec</span> <span class="o">=</span> <span class="n">BinopPrecedence</span><span class="p">[</span><span class="n">CurTok</span><span class="p">];</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><=</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
+  <span class="k">return</span> <span class="n">TokPrec</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// Error* - These are little helper functions for error handling.</span>
+<span class="n">ExprAST</span> <span class="o">*</span><span class="nf">Error</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Error: %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+<span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ErrorP</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+<span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ErrorF</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseExpression</span><span class="p">();</span>
+
+<span class="c1">/// identifierexpr</span>
+<span class="c1">///   ::= identifier</span>
+<span class="c1">///   ::= identifier '(' expression* ')'</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseIdentifierExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat identifier.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'('</span><span class="p">)</span> <span class="c1">// Simple variable ref.</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">VariableExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">);</span>
+
+  <span class="c1">// Call.</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat (</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="n">Args</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Arg</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+      <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Arg</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+      <span class="n">Args</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">Arg</span><span class="p">);</span>
+
+      <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">')'</span><span class="p">)</span>
+        <span class="k">break</span><span class="p">;</span>
+
+      <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span>
+        <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"Expected ')' or ',' in argument list"</span><span class="p">);</span>
+      <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Eat the ')'.</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">CallExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">,</span> <span class="n">Args</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// numberexpr ::= number</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseNumberExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Result</span> <span class="o">=</span> <span class="k">new</span> <span class="n">NumberExprAST</span><span class="p">(</span><span class="n">NumVal</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// consume the number</span>
+  <span class="k">return</span> <span class="n">Result</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// parenexpr ::= '(' expression ')'</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseParenExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat (.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">V</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">V</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected ')'"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat ).</span>
+  <span class="k">return</span> <span class="n">V</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// ifexpr ::= 'if' expression 'then' expression 'else' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseIfExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the if.</span>
+
+  <span class="c1">// condition.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Cond</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Cond</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_then</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected then"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the then</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Then</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Then</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_else</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected else"</span><span class="p">);</span>
+
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Else</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Else</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">IfExprAST</span><span class="p">(</span><span class="n">Cond</span><span class="p">,</span> <span class="n">Then</span><span class="p">,</span> <span class="n">Else</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseForExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the for.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected identifier after for"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat identifier.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'='</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected '=' after for"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat '='.</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Start</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Start</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected ',' after for start value"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">End</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">End</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// The step value is optional.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Step</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">','</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="n">Step</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Step</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_in</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected 'in' after for"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat 'in'.</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Body</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">ForExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">,</span> <span class="n">Start</span><span class="p">,</span> <span class="n">End</span><span class="p">,</span> <span class="n">Step</span><span class="p">,</span> <span class="n">Body</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// varexpr ::= 'var' identifier ('=' expression)?</span>
+<span class="c1">//                    (',' identifier ('=' expression)?)* 'in' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseVarExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the var.</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">pair</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*></span> <span class="o">></span> <span class="n">VarNames</span><span class="p">;</span>
+
+  <span class="c1">// At least one variable name is required.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected identifier after var"</span><span class="p">);</span>
+
+  <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat identifier.</span>
+
+    <span class="c1">// Read the optional initializer.</span>
+    <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Init</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">'='</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the '='.</span>
+
+      <span class="n">Init</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">Init</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+
+    <span class="n">VarNames</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">make_pair</span><span class="p">(</span><span class="n">Name</span><span class="p">,</span> <span class="n">Init</span><span class="p">));</span>
+
+    <span class="c1">// End of var list, exit loop.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the ','.</span>
+
+    <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected identifier list after var"</span><span class="p">);</span>
+  <span class="p">}</span>
+
+  <span class="c1">// At this point, we have to have 'in'.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_in</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected 'in' keyword after 'var'"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat 'in'.</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Body</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">VarExprAST</span><span class="p">(</span><span class="n">VarNames</span><span class="p">,</span> <span class="n">Body</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// primary</span>
+<span class="c1">///   ::= identifierexpr</span>
+<span class="c1">///   ::= numberexpr</span>
+<span class="c1">///   ::= parenexpr</span>
+<span class="c1">///   ::= ifexpr</span>
+<span class="c1">///   ::= forexpr</span>
+<span class="c1">///   ::= varexpr</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParsePrimary</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="nl">default:</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"unknown token when expecting an expression"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>:
+    <span class="k">return</span> <span class="n">ParseIdentifierExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_number</span>:
+    <span class="k">return</span> <span class="n">ParseNumberExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="sc">'('</span>:
+    <span class="k">return</span> <span class="n">ParseParenExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_if</span>:
+    <span class="k">return</span> <span class="n">ParseIfExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_for</span>:
+    <span class="k">return</span> <span class="n">ParseForExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_var</span>:
+    <span class="k">return</span> <span class="n">ParseVarExpr</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// unary</span>
+<span class="c1">///   ::= primary</span>
+<span class="c1">///   ::= '!' unary</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseUnary</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// If the current token is not an operator, it must be a primary expr.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="o">||</span> <span class="n">CurTok</span> <span class="o">==</span> <span class="sc">'('</span> <span class="o">||</span> <span class="n">CurTok</span> <span class="o">==</span> <span class="sc">','</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ParsePrimary</span><span class="p">();</span>
+
+  <span class="c1">// If this is a unary operator, read it.</span>
+  <span class="kt">int</span> <span class="n">Opc</span> <span class="o">=</span> <span class="n">CurTok</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">Operand</span> <span class="o">=</span> <span class="n">ParseUnary</span><span class="p">())</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">UnaryExprAST</span><span class="p">(</span><span class="n">Opc</span><span class="p">,</span> <span class="n">Operand</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// binoprhs</span>
+<span class="c1">///   ::= ('+' unary)*</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseBinOpRHS</span><span class="p">(</span><span class="kt">int</span> <span class="n">ExprPrec</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span><span class="p">)</span> <span class="p">{</span>
+  <span class="c1">// If this is a binop, find its precedence.</span>
+  <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+    <span class="kt">int</span> <span class="n">TokPrec</span> <span class="o">=</span> <span class="n">GetTokPrecedence</span><span class="p">();</span>
+
+    <span class="c1">// If this is a binop that binds at least as tightly as the current binop,</span>
+    <span class="c1">// consume it, otherwise we are done.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><</span> <span class="n">ExprPrec</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">LHS</span><span class="p">;</span>
+
+    <span class="c1">// Okay, we know this is a binop.</span>
+    <span class="kt">int</span> <span class="n">BinOp</span> <span class="o">=</span> <span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat binop</span>
+
+    <span class="c1">// Parse the unary expression after the binary operator.</span>
+    <span class="n">ExprAST</span> <span class="o">*</span><span class="n">RHS</span> <span class="o">=</span> <span class="n">ParseUnary</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">RHS</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+    <span class="c1">// If BinOp binds less tightly with RHS than the operator after RHS, let</span>
+    <span class="c1">// the pending operator take RHS as its LHS.</span>
+    <span class="kt">int</span> <span class="n">NextPrec</span> <span class="o">=</span> <span class="n">GetTokPrecedence</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><</span> <span class="n">NextPrec</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">RHS</span> <span class="o">=</span> <span class="n">ParseBinOpRHS</span><span class="p">(</span><span class="n">TokPrec</span> <span class="o">+</span> <span class="mi">1</span><span class="p">,</span> <span class="n">RHS</span><span class="p">);</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">RHS</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+
+    <span class="c1">// Merge LHS/RHS.</span>
+    <span class="n">LHS</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BinaryExprAST</span><span class="p">(</span><span class="n">BinOp</span><span class="p">,</span> <span class="n">LHS</span><span class="p">,</span> <span class="n">RHS</span><span class="p">);</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// expression</span>
+<span class="c1">///   ::= unary binoprhs</span>
+<span class="c1">///</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseExpression</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span> <span class="o">=</span> <span class="n">ParseUnary</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">LHS</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="n">ParseBinOpRHS</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">LHS</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// prototype</span>
+<span class="c1">///   ::= id '(' id* ')'</span>
+<span class="c1">///   ::= binary LETTER number? (id, id)</span>
+<span class="c1">///   ::= unary LETTER (id)</span>
+<span class="k">static</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ParsePrototype</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">FnName</span><span class="p">;</span>
+
+  <span class="kt">unsigned</span> <span class="n">Kind</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="c1">// 0 = identifier, 1 = unary, 2 = binary.</span>
+  <span class="kt">unsigned</span> <span class="n">BinaryPrecedence</span> <span class="o">=</span> <span class="mi">30</span><span class="p">;</span>
+
+  <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="nl">default:</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected function name in prototype"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>:
+    <span class="n">FnName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_unary</span>:
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+      <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected unary operator"</span><span class="p">);</span>
+    <span class="n">FnName</span> <span class="o">=</span> <span class="s">"unary"</span><span class="p">;</span>
+    <span class="n">FnName</span> <span class="o">+=</span> <span class="p">(</span><span class="kt">char</span><span class="p">)</span><span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_binary</span>:
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+      <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected binary operator"</span><span class="p">);</span>
+    <span class="n">FnName</span> <span class="o">=</span> <span class="s">"binary"</span><span class="p">;</span>
+    <span class="n">FnName</span> <span class="o">+=</span> <span class="p">(</span><span class="kt">char</span><span class="p">)</span><span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+
+    <span class="c1">// Read the precedence if present.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="n">tok_number</span><span class="p">)</span> <span class="p">{</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">NumVal</span> <span class="o"><</span> <span class="mi">1</span> <span class="o">||</span> <span class="n">NumVal</span> <span class="o">></span> <span class="mi">100</span><span class="p">)</span>
+        <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Invalid precedecnce: must be 1..100"</span><span class="p">);</span>
+      <span class="n">BinaryPrecedence</span> <span class="o">=</span> <span class="p">(</span><span class="kt">unsigned</span><span class="p">)</span><span class="n">NumVal</span><span class="p">;</span>
+      <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="p">}</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'('</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected '(' in prototype"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">ArgNames</span><span class="p">;</span>
+  <span class="k">while</span> <span class="p">(</span><span class="n">getNextToken</span><span class="p">()</span> <span class="o">==</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="n">ArgNames</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">IdentifierStr</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected ')' in prototype"</span><span class="p">);</span>
+
+  <span class="c1">// success.</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat ')'.</span>
+
+  <span class="c1">// Verify right number of names for operator.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Kind</span> <span class="o">&&</span> <span class="n">ArgNames</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Kind</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Invalid number of operands for operator"</span><span class="p">);</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">PrototypeAST</span><span class="p">(</span><span class="n">FnName</span><span class="p">,</span> <span class="n">ArgNames</span><span class="p">,</span> <span class="n">Kind</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">BinaryPrecedence</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// definition ::= 'def' prototype expression</span>
+<span class="k">static</span> <span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ParseDefinition</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat def.</span>
+  <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span> <span class="o">=</span> <span class="n">ParsePrototype</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Proto</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">E</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">())</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">FunctionAST</span><span class="p">(</span><span class="n">Proto</span><span class="p">,</span> <span class="n">E</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// toplevelexpr ::= expression</span>
+<span class="k">static</span> <span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ParseTopLevelExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">E</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">())</span> <span class="p">{</span>
+    <span class="c1">// Make an anonymous proto.</span>
+    <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span> <span class="o">=</span> <span class="k">new</span> <span class="n">PrototypeAST</span><span class="p">(</span><span class="s">""</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="p">());</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">FunctionAST</span><span class="p">(</span><span class="n">Proto</span><span class="p">,</span> <span class="n">E</span><span class="p">);</span>
+  <span class="p">}</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// external ::= 'extern' prototype</span>
+<span class="k">static</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ParseExtern</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat extern.</span>
+  <span class="k">return</span> <span class="n">ParsePrototype</span><span class="p">();</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Code Generation</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="k">static</span> <span class="n">Module</span> <span class="o">*</span><span class="n">TheModule</span><span class="p">;</span>
+<span class="k">static</span> <span class="n">IRBuilder</span><span class="o"><></span> <span class="n">Builder</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">());</span>
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">AllocaInst</span> <span class="o">*></span> <span class="n">NamedValues</span><span class="p">;</span>
+<span class="k">static</span> <span class="n">legacy</span><span class="o">::</span><span class="n">FunctionPassManager</span> <span class="o">*</span><span class="n">TheFPM</span><span class="p">;</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="nf">ErrorV</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of</span>
+<span class="c1">/// the function.  This is used for mutable variables etc.</span>
+<span class="k">static</span> <span class="n">AllocaInst</span> <span class="o">*</span><span class="nf">CreateEntryBlockAlloca</span><span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span><span class="p">,</span>
+                                          <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">VarName</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">IRBuilder</span><span class="o"><></span> <span class="n">TmpB</span><span class="p">(</span><span class="o">&</span><span class="n">TheFunction</span><span class="o">-></span><span class="n">getEntryBlock</span><span class="p">(),</span>
+                   <span class="n">TheFunction</span><span class="o">-></span><span class="n">getEntryBlock</span><span class="p">().</span><span class="n">begin</span><span class="p">());</span>
+  <span class="k">return</span> <span class="n">TmpB</span><span class="p">.</span><span class="n">CreateAlloca</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="mi">0</span><span class="p">,</span>
+                           <span class="n">VarName</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">NumberExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">return</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="n">Val</span><span class="p">));</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">VariableExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Look this variable up in the function.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">V</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">Name</span><span class="p">];</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">V</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown variable name"</span><span class="p">);</span>
+
+  <span class="c1">// Load the value.</span>
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateLoad</span><span class="p">(</span><span class="n">V</span><span class="p">,</span> <span class="n">Name</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">UnaryExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">OperandV</span> <span class="o">=</span> <span class="n">Operand</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">OperandV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">(</span><span class="s">"unary"</span><span class="p">)</span> <span class="o">+</span> <span class="n">Opcode</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">F</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown unary operator"</span><span class="p">);</span>
+
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">F</span><span class="p">,</span> <span class="n">OperandV</span><span class="p">,</span> <span class="s">"unop"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">BinaryExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Special case '=' because we don't want to emit the LHS as an expression.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Op</span> <span class="o">==</span> <span class="sc">'='</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Assignment requires the LHS to be an identifier.</span>
+    <span class="c1">// This assume we're building without RTTI because LLVM builds that way by</span>
+    <span class="c1">// default.  If you build LLVM with RTTI this can be changed to a</span>
+    <span class="c1">// dynamic_cast for automatic error checking.</span>
+    <span class="n">VariableExprAST</span> <span class="o">*</span><span class="n">LHSE</span> <span class="o">=</span> <span class="k">static_cast</span><span class="o"><</span><span class="n">VariableExprAST</span> <span class="o">*></span><span class="p">(</span><span class="n">LHS</span><span class="p">);</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">LHSE</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"destination of '=' must be a variable"</span><span class="p">);</span>
+    <span class="c1">// Codegen the RHS.</span>
+    <span class="n">Value</span> <span class="o">*</span><span class="n">Val</span> <span class="o">=</span> <span class="n">RHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Val</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+    <span class="c1">// Look up the name.</span>
+    <span class="n">Value</span> <span class="o">*</span><span class="n">Variable</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">LHSE</span><span class="o">-></span><span class="n">getName</span><span class="p">()];</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Variable</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown variable name"</span><span class="p">);</span>
+
+    <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">Val</span><span class="p">,</span> <span class="n">Variable</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">Val</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">L</span> <span class="o">=</span> <span class="n">LHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">R</span> <span class="o">=</span> <span class="n">RHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">L</span> <span class="o">==</span> <span class="mi">0</span> <span class="o">||</span> <span class="n">R</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">switch</span> <span class="p">(</span><span class="n">Op</span><span class="p">)</span> <span class="p">{</span>
+  <span class="k">case</span> <span class="sc">'+'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFAdd</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"addtmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'-'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFSub</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"subtmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'*'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFMul</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"multmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'<'</span>:
+    <span class="n">L</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpULT</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"cmptmp"</span><span class="p">);</span>
+    <span class="c1">// Convert bool 0/1 to double 0.0 or 1.0</span>
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateUIToFP</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span>
+                                <span class="s">"booltmp"</span><span class="p">);</span>
+  <span class="nl">default:</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="c1">// If it wasn't a builtin binary operator, it must be a user defined one. Emit</span>
+  <span class="c1">// a call to it.</span>
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">(</span><span class="s">"binary"</span><span class="p">)</span> <span class="o">+</span> <span class="n">Op</span><span class="p">);</span>
+  <span class="n">assert</span><span class="p">(</span><span class="n">F</span> <span class="o">&&</span> <span class="s">"binary operator not found!"</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Ops</span><span class="p">[]</span> <span class="o">=</span> <span class="p">{</span> <span class="n">L</span><span class="p">,</span> <span class="n">R</span> <span class="p">};</span>
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">F</span><span class="p">,</span> <span class="n">Ops</span><span class="p">,</span> <span class="s">"binop"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">CallExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Look up the name in the global module table.</span>
+  <span class="n">Function</span> <span class="o">*</span><span class="n">CalleeF</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">Callee</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CalleeF</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown function referenced"</span><span class="p">);</span>
+
+  <span class="c1">// If argument mismatch error.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CalleeF</span><span class="o">-></span><span class="n">arg_size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">())</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Incorrect # arguments passed"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">Value</span> <span class="o">*></span> <span class="n">ArgsV</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">ArgsV</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">Args</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="o">-></span><span class="n">Codegen</span><span class="p">());</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">ArgsV</span><span class="p">.</span><span class="n">back</span><span class="p">()</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">CalleeF</span><span class="p">,</span> <span class="n">ArgsV</span><span class="p">,</span> <span class="s">"calltmp"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">IfExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">CondV</span> <span class="o">=</span> <span class="n">Cond</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CondV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Convert condition to a bool by comparing equal to 0.0.</span>
+  <span class="n">CondV</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpONE</span><span class="p">(</span>
+      <span class="n">CondV</span><span class="p">,</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">)),</span> <span class="s">"ifcond"</span><span class="p">);</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+
+  <span class="c1">// Create blocks for the then and else cases.  Insert the 'then' block at the</span>
+  <span class="c1">// end of the function.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">ThenBB</span> <span class="o">=</span>
+      <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"then"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">ElseBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"else"</span><span class="p">);</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">MergeBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"ifcont"</span><span class="p">);</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCondBr</span><span class="p">(</span><span class="n">CondV</span><span class="p">,</span> <span class="n">ThenBB</span><span class="p">,</span> <span class="n">ElseBB</span><span class="p">);</span>
+
+  <span class="c1">// Emit then value.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">ThenBB</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">ThenV</span> <span class="o">=</span> <span class="n">Then</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ThenV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="c1">// Codegen of 'Then' can change the current block, update ThenBB for the PHI.</span>
+  <span class="n">ThenBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+
+  <span class="c1">// Emit else block.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">getBasicBlockList</span><span class="p">().</span><span class="n">push_back</span><span class="p">(</span><span class="n">ElseBB</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">ElseBB</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">ElseV</span> <span class="o">=</span> <span class="n">Else</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ElseV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="c1">// Codegen of 'Else' can change the current block, update ElseBB for the PHI.</span>
+  <span class="n">ElseBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+
+  <span class="c1">// Emit merge block.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">getBasicBlockList</span><span class="p">().</span><span class="n">push_back</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="n">PHINode</span> <span class="o">*</span><span class="n">PN</span> <span class="o">=</span>
+      <span class="n">Builder</span><span class="p">.</span><span class="n">CreatePHI</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="mi">2</span><span class="p">,</span> <span class="s">"iftmp"</span><span class="p">);</span>
+
+  <span class="n">PN</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">ThenV</span><span class="p">,</span> <span class="n">ThenBB</span><span class="p">);</span>
+  <span class="n">PN</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">ElseV</span><span class="p">,</span> <span class="n">ElseBB</span><span class="p">);</span>
+  <span class="k">return</span> <span class="n">PN</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">ForExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Output this as:</span>
+  <span class="c1">//   var = alloca double</span>
+  <span class="c1">//   ...</span>
+  <span class="c1">//   start = startexpr</span>
+  <span class="c1">//   store start -> var</span>
+  <span class="c1">//   goto loop</span>
+  <span class="c1">// loop:</span>
+  <span class="c1">//   ...</span>
+  <span class="c1">//   bodyexpr</span>
+  <span class="c1">//   ...</span>
+  <span class="c1">// loopend:</span>
+  <span class="c1">//   step = stepexpr</span>
+  <span class="c1">//   endcond = endexpr</span>
+  <span class="c1">//</span>
+  <span class="c1">//   curvar = load var</span>
+  <span class="c1">//   nextvar = curvar + step</span>
+  <span class="c1">//   store nextvar -> var</span>
+  <span class="c1">//   br endcond, loop, endloop</span>
+  <span class="c1">// outloop:</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+
+  <span class="c1">// Create an alloca for the variable in the entry block.</span>
+  <span class="n">AllocaInst</span> <span class="o">*</span><span class="n">Alloca</span> <span class="o">=</span> <span class="n">CreateEntryBlockAlloca</span><span class="p">(</span><span class="n">TheFunction</span><span class="p">,</span> <span class="n">VarName</span><span class="p">);</span>
+
+  <span class="c1">// Emit the start code first, without 'variable' in scope.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">StartVal</span> <span class="o">=</span> <span class="n">Start</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">StartVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Store the value into the alloca.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">StartVal</span><span class="p">,</span> <span class="n">Alloca</span><span class="p">);</span>
+
+  <span class="c1">// Make the new basic block for the loop header, inserting after current</span>
+  <span class="c1">// block.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">LoopBB</span> <span class="o">=</span>
+      <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"loop"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+
+  <span class="c1">// Insert an explicit fall through from the current block to the LoopBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">LoopBB</span><span class="p">);</span>
+
+  <span class="c1">// Start insertion in LoopBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">LoopBB</span><span class="p">);</span>
+
+  <span class="c1">// Within the loop, the variable is defined equal to the PHI node.  If it</span>
+  <span class="c1">// shadows an existing variable, we have to restore it, so save it now.</span>
+  <span class="n">AllocaInst</span> <span class="o">*</span><span class="n">OldVal</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">];</span>
+  <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">Alloca</span><span class="p">;</span>
+
+  <span class="c1">// Emit the body of the loop.  This, like any other expr, can change the</span>
+  <span class="c1">// current BB.  Note that we ignore the value computed by the body, but don't</span>
+  <span class="c1">// allow an error.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">()</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Emit the step value.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">StepVal</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Step</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">StepVal</span> <span class="o">=</span> <span class="n">Step</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">StepVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// If not specified, use 1.0.</span>
+    <span class="n">StepVal</span> <span class="o">=</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">1.0</span><span class="p">));</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Compute the end condition.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">EndCond</span> <span class="o">=</span> <span class="n">End</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">EndCond</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">EndCond</span><span class="p">;</span>
+
+  <span class="c1">// Reload, increment, and restore the alloca.  This handles the case where</span>
+  <span class="c1">// the body of the loop mutates the variable.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">CurVar</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateLoad</span><span class="p">(</span><span class="n">Alloca</span><span class="p">,</span> <span class="n">VarName</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">NextVar</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFAdd</span><span class="p">(</span><span class="n">CurVar</span><span class="p">,</span> <span class="n">StepVal</span><span class="p">,</span> <span class="s">"nextvar"</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">NextVar</span><span class="p">,</span> <span class="n">Alloca</span><span class="p">);</span>
+
+  <span class="c1">// Convert condition to a bool by comparing equal to 0.0.</span>
+  <span class="n">EndCond</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpONE</span><span class="p">(</span>
+      <span class="n">EndCond</span><span class="p">,</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">)),</span> <span class="s">"loopcond"</span><span class="p">);</span>
+
+  <span class="c1">// Create the "after loop" block and insert it.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">AfterBB</span> <span class="o">=</span>
+      <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"afterloop"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+
+  <span class="c1">// Insert the conditional branch into the end of LoopEndBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCondBr</span><span class="p">(</span><span class="n">EndCond</span><span class="p">,</span> <span class="n">LoopBB</span><span class="p">,</span> <span class="n">AfterBB</span><span class="p">);</span>
+
+  <span class="c1">// Any new code will be inserted in AfterBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">AfterBB</span><span class="p">);</span>
+
+  <span class="c1">// Restore the unshadowed variable.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">OldVal</span><span class="p">)</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">OldVal</span><span class="p">;</span>
+  <span class="k">else</span>
+    <span class="n">NamedValues</span><span class="p">.</span><span class="n">erase</span><span class="p">(</span><span class="n">VarName</span><span class="p">);</span>
+
+  <span class="c1">// for expr always returns 0.0.</span>
+  <span class="k">return</span> <span class="n">Constant</span><span class="o">::</span><span class="n">getNullValue</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()));</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">VarExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">AllocaInst</span> <span class="o">*></span> <span class="n">OldBindings</span><span class="p">;</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+
+  <span class="c1">// Register all variables and emit their initializer.</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">VarNames</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">VarName</span> <span class="o">=</span> <span class="n">VarNames</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">first</span><span class="p">;</span>
+    <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Init</span> <span class="o">=</span> <span class="n">VarNames</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">second</span><span class="p">;</span>
+
+    <span class="c1">// Emit the initializer before adding the variable to scope, this prevents</span>
+    <span class="c1">// the initializer from referencing the variable itself, and permits stuff</span>
+    <span class="c1">// like this:</span>
+    <span class="c1">//  var a = 1 in</span>
+    <span class="c1">//    var a = a in ...   # refers to outer 'a'.</span>
+    <span class="n">Value</span> <span class="o">*</span><span class="n">InitVal</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Init</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">InitVal</span> <span class="o">=</span> <span class="n">Init</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">InitVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span> <span class="k">else</span> <span class="p">{</span> <span class="c1">// If not specified, use 0.0.</span>
+      <span class="n">InitVal</span> <span class="o">=</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">));</span>
+    <span class="p">}</span>
+
+    <span class="n">AllocaInst</span> <span class="o">*</span><span class="n">Alloca</span> <span class="o">=</span> <span class="n">CreateEntryBlockAlloca</span><span class="p">(</span><span class="n">TheFunction</span><span class="p">,</span> <span class="n">VarName</span><span class="p">);</span>
+    <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">InitVal</span><span class="p">,</span> <span class="n">Alloca</span><span class="p">);</span>
+
+    <span class="c1">// Remember the old variable binding so that we can restore the binding when</span>
+    <span class="c1">// we unrecurse.</span>
+    <span class="n">OldBindings</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]);</span>
+
+    <span class="c1">// Remember this binding.</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">Alloca</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Codegen the body, now that all vars are in scope.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">BodyVal</span> <span class="o">=</span> <span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">BodyVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Pop all our variables from scope.</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">VarNames</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarNames</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">first</span><span class="p">]</span> <span class="o">=</span> <span class="n">OldBindings</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
+
+  <span class="c1">// Return the body computation.</span>
+  <span class="k">return</span> <span class="n">BodyVal</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Function</span> <span class="o">*</span><span class="n">PrototypeAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Make the function type:  double(double,double) etc.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">Type</span> <span class="o">*></span> <span class="n">Doubles</span><span class="p">(</span><span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">(),</span>
+                              <span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()));</span>
+  <span class="n">FunctionType</span> <span class="o">*</span><span class="n">FT</span> <span class="o">=</span>
+      <span class="n">FunctionType</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="n">Doubles</span><span class="p">,</span> <span class="nb">false</span><span class="p">);</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span>
+      <span class="n">Function</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">FT</span><span class="p">,</span> <span class="n">Function</span><span class="o">::</span><span class="n">ExternalLinkage</span><span class="p">,</span> <span class="n">Name</span><span class="p">,</span> <span class="n">TheModule</span><span class="p">);</span>
+
+  <span class="c1">// If F conflicted, there was already something named 'Name'.  If it has a</span>
+  <span class="c1">// body, don't allow redefinition or reextern.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">F</span><span class="o">-></span><span class="n">getName</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Name</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Delete the one we just made and get the existing one.</span>
+    <span class="n">F</span><span class="o">-></span><span class="n">eraseFromParent</span><span class="p">();</span>
+    <span class="n">F</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">Name</span><span class="p">);</span>
+
+    <span class="c1">// If F already has a body, reject this.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">F</span><span class="o">-></span><span class="n">empty</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">ErrorF</span><span class="p">(</span><span class="s">"redefinition of function"</span><span class="p">);</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+
+    <span class="c1">// If F took a different number of args, reject.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">F</span><span class="o">-></span><span class="n">arg_size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">ErrorF</span><span class="p">(</span><span class="s">"redefinition of function with different # args"</span><span class="p">);</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Set names for all arguments.</span>
+  <span class="kt">unsigned</span> <span class="n">Idx</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="n">Function</span><span class="o">::</span><span class="n">arg_iterator</span> <span class="n">AI</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">arg_begin</span><span class="p">();</span> <span class="n">Idx</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span>
+       <span class="o">++</span><span class="n">AI</span><span class="p">,</span> <span class="o">++</span><span class="n">Idx</span><span class="p">)</span>
+    <span class="n">AI</span><span class="o">-></span><span class="n">setName</span><span class="p">(</span><span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]);</span>
+
+  <span class="k">return</span> <span class="n">F</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// CreateArgumentAllocas - Create an alloca for each argument and register the</span>
+<span class="c1">/// argument in the symbol table so that references to it will succeed.</span>
+<span class="kt">void</span> <span class="n">PrototypeAST</span><span class="o">::</span><span class="n">CreateArgumentAllocas</span><span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">F</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Function</span><span class="o">::</span><span class="n">arg_iterator</span> <span class="n">AI</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">arg_begin</span><span class="p">();</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">Idx</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">Idx</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">Idx</span><span class="p">,</span> <span class="o">++</span><span class="n">AI</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Create an alloca for this variable.</span>
+    <span class="n">AllocaInst</span> <span class="o">*</span><span class="n">Alloca</span> <span class="o">=</span> <span class="n">CreateEntryBlockAlloca</span><span class="p">(</span><span class="n">F</span><span class="p">,</span> <span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]);</span>
+
+    <span class="c1">// Store the initial value into the alloca.</span>
+    <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">AI</span><span class="p">,</span> <span class="n">Alloca</span><span class="p">);</span>
+
+    <span class="c1">// Add arguments to variable symbol table.</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]]</span> <span class="o">=</span> <span class="n">Alloca</span><span class="p">;</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="n">Function</span> <span class="o">*</span><span class="n">FunctionAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">NamedValues</span><span class="p">.</span><span class="n">clear</span><span class="p">();</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Proto</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">TheFunction</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// If this is an operator, install it.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Proto</span><span class="o">-></span><span class="n">isBinaryOp</span><span class="p">())</span>
+    <span class="n">BinopPrecedence</span><span class="p">[</span><span class="n">Proto</span><span class="o">-></span><span class="n">getOperatorName</span><span class="p">()]</span> <span class="o">=</span> <span class="n">Proto</span><span class="o">-></span><span class="n">getBinaryPrecedence</span><span class="p">();</span>
+
+  <span class="c1">// Create a new basic block to start insertion into.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">BB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"entry"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">BB</span><span class="p">);</span>
+
+  <span class="c1">// Add all arguments to the symbol table and create their allocas.</span>
+  <span class="n">Proto</span><span class="o">-></span><span class="n">CreateArgumentAllocas</span><span class="p">(</span><span class="n">TheFunction</span><span class="p">);</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">Value</span> <span class="o">*</span><span class="n">RetVal</span> <span class="o">=</span> <span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+    <span class="c1">// Finish off the function.</span>
+    <span class="n">Builder</span><span class="p">.</span><span class="n">CreateRet</span><span class="p">(</span><span class="n">RetVal</span><span class="p">);</span>
+
+    <span class="c1">// Validate the generated code, checking for consistency.</span>
+    <span class="n">verifyFunction</span><span class="p">(</span><span class="o">*</span><span class="n">TheFunction</span><span class="p">);</span>
+
+    <span class="c1">// Optimize the function.</span>
+    <span class="n">TheFPM</span><span class="o">-></span><span class="n">run</span><span class="p">(</span><span class="o">*</span><span class="n">TheFunction</span><span class="p">);</span>
+
+    <span class="k">return</span> <span class="n">TheFunction</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Error reading body, remove function.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">eraseFromParent</span><span class="p">();</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">Proto</span><span class="o">-></span><span class="n">isBinaryOp</span><span class="p">())</span>
+    <span class="n">BinopPrecedence</span><span class="p">.</span><span class="n">erase</span><span class="p">(</span><span class="n">Proto</span><span class="o">-></span><span class="n">getOperatorName</span><span class="p">());</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Top-Level parsing and JIT Driver</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="k">static</span> <span class="n">ExecutionEngine</span> <span class="o">*</span><span class="n">TheExecutionEngine</span><span class="p">;</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleDefinition</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">FunctionAST</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">ParseDefinition</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">LF</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Read function definition:"</span><span class="p">);</span>
+      <span class="n">LF</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleExtern</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">P</span> <span class="o">=</span> <span class="n">ParseExtern</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">P</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Read extern: "</span><span class="p">);</span>
+      <span class="n">F</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleTopLevelExpression</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Evaluate a top-level expression into an anonymous function.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">FunctionAST</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">ParseTopLevelExpr</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">LF</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">finalizeObject</span><span class="p">();</span>
+      <span class="c1">// JIT the function, returning a function pointer.</span>
+      <span class="kt">void</span> <span class="o">*</span><span class="n">FPtr</span> <span class="o">=</span> <span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">getPointerToFunction</span><span class="p">(</span><span class="n">LF</span><span class="p">);</span>
+
+      <span class="c1">// Cast it to the right type (takes no arguments, returns a double) so we</span>
+      <span class="c1">// can call it as a native function.</span>
+      <span class="kt">double</span> <span class="p">(</span><span class="o">*</span><span class="n">FP</span><span class="p">)()</span> <span class="o">=</span> <span class="p">(</span><span class="kt">double</span> <span class="p">(</span><span class="o">*</span><span class="p">)())(</span><span class="kt">intptr_t</span><span class="p">)</span><span class="n">FPtr</span><span class="p">;</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Evaluated to %f</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">FP</span><span class="p">());</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// top ::= definition | external | expression | ';'</span>
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">MainLoop</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"ready> "</span><span class="p">);</span>
+    <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">case</span> <span class="n">tok_eof</span>:
+      <span class="k">return</span><span class="p">;</span>
+    <span class="k">case</span> <span class="sc">';'</span>:
+      <span class="n">getNextToken</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span> <span class="c1">// ignore top-level semicolons.</span>
+    <span class="k">case</span> <span class="n">tok_def</span>:
+      <span class="n">HandleDefinition</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="k">case</span> <span class="n">tok_extern</span>:
+      <span class="n">HandleExtern</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="nl">default:</span>
+      <span class="n">HandleTopLevelExpression</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// "Library" functions that can be "extern'd" from user code.</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">/// putchard - putchar that takes a double and returns 0.</span>
+<span class="k">extern</span> <span class="s">"C"</span> <span class="kt">double</span> <span class="n">putchard</span><span class="p">(</span><span class="kt">double</span> <span class="n">X</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">putchar</span><span class="p">((</span><span class="kt">char</span><span class="p">)</span><span class="n">X</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// printd - printf that takes a double prints it as "%f\n", returning 0.</span>
+<span class="k">extern</span> <span class="s">"C"</span> <span class="kt">double</span> <span class="n">printd</span><span class="p">(</span><span class="kt">double</span> <span class="n">X</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">printf</span><span class="p">(</span><span class="s">"%f</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">X</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Main driver code.</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="kt">int</span> <span class="n">main</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">InitializeNativeTarget</span><span class="p">();</span>
+  <span class="n">InitializeNativeTargetAsmPrinter</span><span class="p">();</span>
+  <span class="n">InitializeNativeTargetAsmParser</span><span class="p">();</span>
+  <span class="n">LLVMContext</span> <span class="o">&</span><span class="n">Context</span> <span class="o">=</span> <span class="n">getGlobalContext</span><span class="p">();</span>
+
+  <span class="c1">// Install standard binary operators.</span>
+  <span class="c1">// 1 is lowest precedence.</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'='</span><span class="p">]</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'<'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'+'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'-'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'*'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">40</span><span class="p">;</span> <span class="c1">// highest.</span>
+
+  <span class="c1">// Prime the first token.</span>
+  <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"ready> "</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="c1">// Make the module, which holds all the code.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">unique_ptr</span><span class="o"><</span><span class="n">Module</span><span class="o">></span> <span class="n">Owner</span> <span class="o">=</span> <span class="n">make_unique</span><span class="o"><</span><span class="n">Module</span><span class="o">></span><span class="p">(</span><span class="s">"my cool jit"</span><span class="p">,</span> <span class="n">Context</span><span class="p">);</span>
+  <span class="n">TheModule</span> <span class="o">=</span> <span class="n">Owner</span><span class="p">.</span><span class="n">get</span><span class="p">();</span>
+
+  <span class="c1">// Create the JIT.  This takes ownership of the module.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">ErrStr</span><span class="p">;</span>
+  <span class="n">TheExecutionEngine</span> <span class="o">=</span>
+      <span class="n">EngineBuilder</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">move</span><span class="p">(</span><span class="n">Owner</span><span class="p">))</span>
+          <span class="p">.</span><span class="n">setErrorStr</span><span class="p">(</span><span class="o">&</span><span class="n">ErrStr</span><span class="p">)</span>
+          <span class="p">.</span><span class="n">setMCJITMemoryManager</span><span class="p">(</span><span class="n">llvm</span><span class="o">::</span><span class="n">make_unique</span><span class="o"><</span><span class="n">SectionMemoryManager</span><span class="o">></span><span class="p">())</span>
+          <span class="p">.</span><span class="n">create</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">TheExecutionEngine</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Could not create ExecutionEngine: %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">ErrStr</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+    <span class="n">exit</span><span class="p">(</span><span class="mi">1</span><span class="p">);</span>
+  <span class="p">}</span>
+
+  <span class="n">legacy</span><span class="o">::</span><span class="n">FunctionPassManager</span> <span class="n">OurFPM</span><span class="p">(</span><span class="n">TheModule</span><span class="p">);</span>
+
+  <span class="c1">// Set up the optimizer pipeline.  Start with registering info about how the</span>
+  <span class="c1">// target lays out data structures.</span>
+  <span class="n">TheModule</span><span class="o">-></span><span class="n">setDataLayout</span><span class="p">(</span><span class="o">*</span><span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">getDataLayout</span><span class="p">());</span>
+  <span class="c1">// Provide basic AliasAnalysis support for GVN.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createBasicAliasAnalysisPass</span><span class="p">());</span>
+  <span class="c1">// Promote allocas to registers.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createPromoteMemoryToRegisterPass</span><span class="p">());</span>
+  <span class="c1">// Do simple "peephole" optimizations and bit-twiddling optzns.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createInstructionCombiningPass</span><span class="p">());</span>
+  <span class="c1">// Reassociate expressions.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createReassociatePass</span><span class="p">());</span>
+  <span class="c1">// Eliminate Common SubExpressions.</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createGVNPass</span><span class="p">());</span>
+  <span class="c1">// Simplify the control flow graph (deleting unreachable blocks, etc).</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">createCFGSimplificationPass</span><span class="p">());</span>
+
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">doInitialization</span><span class="p">();</span>
+
+  <span class="c1">// Set the global so the code gen can use this.</span>
+  <span class="n">TheFPM</span> <span class="o">=</span> <span class="o">&</span><span class="n">OurFPM</span><span class="p">;</span>
+
+  <span class="c1">// Run the main "interpreter loop" now.</span>
+  <span class="n">MainLoop</span><span class="p">();</span>
+
+  <span class="n">TheFPM</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Print out all of the generated code.</span>
+  <span class="n">TheModule</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p><a class="reference external" href="LangImpl8.html">Next: Adding Debug Information</a></p>
+</div>
+</div>
+
+
+          </div>
+      </div>
+      <div class="clearer"></div>
+    </div>
+    <div class="related">
+      <h3>Navigation</h3>
+      <ul>
+        <li class="right" style="margin-right: 10px">
+          <a href="../genindex.html" title="General Index"
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+        <li class="right" >
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+             >next</a> |</li>
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+  <div class="section" id="kaleidoscope-adding-debug-information">
+<h1>8. Kaleidoscope: Adding Debug Information<a class="headerlink" href="#kaleidoscope-adding-debug-information" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#chapter-8-introduction" id="id1">Chapter 8 Introduction</a></li>
+<li><a class="reference internal" href="#why-is-this-a-hard-problem" id="id2">Why is this a hard problem?</a></li>
+<li><a class="reference internal" href="#ahead-of-time-compilation-mode" id="id3">Ahead-of-Time Compilation Mode</a></li>
+<li><a class="reference internal" href="#compile-unit" id="id4">Compile Unit</a></li>
+<li><a class="reference internal" href="#dwarf-emission-setup" id="id5">DWARF Emission Setup</a></li>
+<li><a class="reference internal" href="#functions" id="id6">Functions</a></li>
+<li><a class="reference internal" href="#source-locations" id="id7">Source Locations</a></li>
+<li><a class="reference internal" href="#variables" id="id8">Variables</a></li>
+<li><a class="reference internal" href="#full-code-listing" id="id9">Full Code Listing</a></li>
+</ul>
+</div>
+<div class="section" id="chapter-8-introduction">
+<h2><a class="toc-backref" href="#id1">8.1. Chapter 8 Introduction</a><a class="headerlink" href="#chapter-8-introduction" title="Permalink to this headline">¶</a></h2>
+<p>Welcome to Chapter 8 of the “<a class="reference external" href="index.html">Implementing a language with
+LLVM</a>” tutorial. In chapters 1 through 7, we’ve built a
+decent little programming language with functions and variables.
+What happens if something goes wrong though, how do you debug your
+program?</p>
+<p>Source level debugging uses formatted data that helps a debugger
+translate from binary and the state of the machine back to the
+source that the programmer wrote. In LLVM we generally use a format
+called <a class="reference external" href="http://dwarfstd.org">DWARF</a>. DWARF is a compact encoding
+that represents types, source locations, and variable locations.</p>
+<p>The short summary of this chapter is that we’ll go through the
+various things you have to add to a programming language to
+support debug info, and how you translate that into DWARF.</p>
+<p>Caveat: For now we can’t debug via the JIT, so we’ll need to compile
+our program down to something small and standalone. As part of this
+we’ll make a few modifications to the running of the language and
+how programs are compiled. This means that we’ll have a source file
+with a simple program written in Kaleidoscope rather than the
+interactive JIT. It does involve a limitation that we can only
+have one “top level” command at a time to reduce the number of
+changes necessary.</p>
+<p>Here’s the sample program we’ll be compiling:</p>
+<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">fib</span><span class="p">(</span><span class="n">x</span><span class="p">)</span>
+  <span class="k">if</span> <span class="n">x</span> <span class="o"><</span> <span class="mi">3</span> <span class="n">then</span>
+    <span class="mi">1</span>
+  <span class="k">else</span>
+    <span class="n">fib</span><span class="p">(</span><span class="n">x</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span><span class="o">+</span><span class="n">fib</span><span class="p">(</span><span class="n">x</span><span class="o">-</span><span class="mi">2</span><span class="p">);</span>
+
+<span class="n">fib</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="why-is-this-a-hard-problem">
+<h2><a class="toc-backref" href="#id2">8.2. Why is this a hard problem?</a><a class="headerlink" href="#why-is-this-a-hard-problem" title="Permalink to this headline">¶</a></h2>
+<p>Debug information is a hard problem for a few different reasons - mostly
+centered around optimized code. First, optimization makes keeping source
+locations more difficult. In LLVM IR we keep the original source location
+for each IR level instruction on the instruction. Optimization passes
+should keep the source locations for newly created instructions, but merged
+instructions only get to keep a single location - this can cause jumping
+around when stepping through optimized programs. Secondly, optimization
+can move variables in ways that are either optimized out, shared in memory
+with other variables, or difficult to track. For the purposes of this
+tutorial we’re going to avoid optimization (as you’ll see with one of the
+next sets of patches).</p>
+</div>
+<div class="section" id="ahead-of-time-compilation-mode">
+<h2><a class="toc-backref" href="#id3">8.3. Ahead-of-Time Compilation Mode</a><a class="headerlink" href="#ahead-of-time-compilation-mode" title="Permalink to this headline">¶</a></h2>
+<p>To highlight only the aspects of adding debug information to a source
+language without needing to worry about the complexities of JIT debugging
+we’re going to make a few changes to Kaleidoscope to support compiling
+the IR emitted by the front end into a simple standalone program that
+you can execute, debug, and see results.</p>
+<p>First we make our anonymous function that contains our top level
+statement be our “main”:</p>
+<div class="highlight-udiff"><div class="highlight"><pre><span class="gd">-    PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());</span>
+<span class="gi">+    PrototypeAST *Proto = new PrototypeAST("main", std::vector<std::string>());</span>
+</pre></div>
+</div>
+<p>just with the simple change of giving it a name.</p>
+<p>Then we’re going to remove the command line code wherever it exists:</p>
+<div class="highlight-udiff"><div class="highlight"><pre><span class="gu">@@ -1129,7 +1129,6 @@ static void HandleTopLevelExpression() {</span>
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+   while (1) {
+<span class="gd">-    fprintf(stderr, "ready> ");</span>
+     switch (CurTok) {
+     case tok_eof:
+       return;
+<span class="gu">@@ -1184,7 +1183,6 @@ int main() {</span>
+   BinopPrecedence['*'] = 40; // highest.
+
+   // Prime the first token.
+<span class="gd">-  fprintf(stderr, "ready> ");</span>
+   getNextToken();
+</pre></div>
+</div>
+<p>Lastly we’re going to disable all of the optimization passes and the JIT so
+that the only thing that happens after we’re done parsing and generating
+code is that the llvm IR goes to standard error:</p>
+<div class="highlight-udiff"><div class="highlight"><pre><span class="gu">@@ -1108,17 +1108,8 @@ static void HandleExtern() {</span>
+ static void HandleTopLevelExpression() {
+   // Evaluate a top-level expression into an anonymous function.
+   if (FunctionAST *F = ParseTopLevelExpr()) {
+<span class="gd">-    if (Function *LF = F->Codegen()) {</span>
+<span class="gd">-      // We're just doing this to make sure it executes.</span>
+<span class="gd">-      TheExecutionEngine->finalizeObject();</span>
+<span class="gd">-      // JIT the function, returning a function pointer.</span>
+<span class="gd">-      void *FPtr = TheExecutionEngine->getPointerToFunction(LF);</span>
+<span class="gd">-</span>
+<span class="gd">-      // Cast it to the right type (takes no arguments, returns a double) so we</span>
+<span class="gd">-      // can call it as a native function.</span>
+<span class="gd">-      double (*FP)() = (double (*)())(intptr_t)FPtr;</span>
+<span class="gd">-      // Ignore the return value for this.</span>
+<span class="gd">-      (void)FP;</span>
+<span class="gi">+    if (!F->Codegen()) {</span>
+<span class="gi">+      fprintf(stderr, "Error generating code for top level expr");</span>
+     }
+   } else {
+     // Skip token for error recovery.
+<span class="gu">@@ -1439,11 +1459,11 @@ int main() {</span>
+   // target lays out data structures.
+   TheModule->setDataLayout(TheExecutionEngine->getDataLayout());
+   OurFPM.add(new DataLayoutPass());
+<span class="gi">+#if 0</span>
+   OurFPM.add(createBasicAliasAnalysisPass());
+   // Promote allocas to registers.
+   OurFPM.add(createPromoteMemoryToRegisterPass());
+<span class="gu">@@ -1218,7 +1210,7 @@ int main() {</span>
+   OurFPM.add(createGVNPass());
+   // Simplify the control flow graph (deleting unreachable blocks, etc).
+   OurFPM.add(createCFGSimplificationPass());
+<span class="gd">-</span>
+<span class="gi">+  #endif</span>
+   OurFPM.doInitialization();
+
+   // Set the global so the code gen can use this.
+</pre></div>
+</div>
+<p>This relatively small set of changes get us to the point that we can compile
+our piece of Kaleidoscope language down to an executable program via this
+command line:</p>
+<div class="highlight-bash"><div class="highlight"><pre>Kaleidoscope-Ch8 < fib.ks | & clang -x ir -
+</pre></div>
+</div>
+<p>which gives an a.out/a.exe in the current working directory.</p>
+</div>
+<div class="section" id="compile-unit">
+<h2><a class="toc-backref" href="#id4">8.4. Compile Unit</a><a class="headerlink" href="#compile-unit" title="Permalink to this headline">¶</a></h2>
+<p>The top level container for a section of code in DWARF is a compile unit.
+This contains the type and function data for an individual translation unit
+(read: one file of source code). So the first thing we need to do is
+construct one for our fib.ks file.</p>
+</div>
+<div class="section" id="dwarf-emission-setup">
+<h2><a class="toc-backref" href="#id5">8.5. DWARF Emission Setup</a><a class="headerlink" href="#dwarf-emission-setup" title="Permalink to this headline">¶</a></h2>
+<p>Similar to the <tt class="docutils literal"><span class="pre">IRBuilder</span></tt> class we have a
+<tt class="docutils literal"><span class="pre">`DIBuilder</span></tt> <<a class="reference external" href="http://llvm.org/doxygen/classllvm_1_1DIBuilder.html">http://llvm.org/doxygen/classllvm_1_1DIBuilder.html</a>>`_ class
+that helps in constructing debug metadata for an llvm IR file. It
+corresponds 1:1 similarly to <tt class="docutils literal"><span class="pre">IRBuilder</span></tt> and llvm IR, but with nicer names.
+Using it does require that you be more familiar with DWARF terminology than
+you needed to be with <tt class="docutils literal"><span class="pre">IRBuilder</span></tt> and <tt class="docutils literal"><span class="pre">Instruction</span></tt> names, but if you
+read through the general documentation on the
+<tt class="docutils literal"><span class="pre">`Metadata</span> <span class="pre">Format</span></tt> <<a class="reference external" href="http://llvm.org/docs/SourceLevelDebugging.html">http://llvm.org/docs/SourceLevelDebugging.html</a>>`_ it
+should be a little more clear. We’ll be using this class to construct all
+of our IR level descriptions. Construction for it takes a module so we
+need to construct it shortly after we construct our module. We’ve left it
+as a global static variable to make it a bit easier to use.</p>
+<p>Next we’re going to create a small container to cache some of our frequent
+data. The first will be our compile unit, but we’ll also write a bit of
+code for our one type since we won’t have to worry about multiple typed
+expressions:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">static</span> <span class="n">DIBuilder</span> <span class="o">*</span><span class="n">DBuilder</span><span class="p">;</span>
+
+<span class="k">struct</span> <span class="n">DebugInfo</span> <span class="p">{</span>
+  <span class="n">DICompileUnit</span> <span class="o">*</span><span class="n">TheCU</span><span class="p">;</span>
+  <span class="n">DIType</span> <span class="o">*</span><span class="n">DblTy</span><span class="p">;</span>
+
+  <span class="n">DIType</span> <span class="o">*</span><span class="nf">getDoubleTy</span><span class="p">();</span>
+<span class="p">}</span> <span class="n">KSDbgInfo</span><span class="p">;</span>
+
+<span class="n">DIType</span> <span class="o">*</span><span class="n">DebugInfo</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">DblTy</span><span class="p">.</span><span class="n">isValid</span><span class="p">())</span>
+    <span class="k">return</span> <span class="n">DblTy</span><span class="p">;</span>
+
+  <span class="n">DblTy</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createBasicType</span><span class="p">(</span><span class="s">"double"</span><span class="p">,</span> <span class="mi">64</span><span class="p">,</span> <span class="mi">64</span><span class="p">,</span> <span class="n">dwarf</span><span class="o">::</span><span class="n">DW_ATE_float</span><span class="p">);</span>
+  <span class="k">return</span> <span class="n">DblTy</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>And then later on in <tt class="docutils literal"><span class="pre">main</span></tt> when we’re constructing our module:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">DBuilder</span> <span class="o">=</span> <span class="k">new</span> <span class="n">DIBuilder</span><span class="p">(</span><span class="o">*</span><span class="n">TheModule</span><span class="p">);</span>
+
+<span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">TheCU</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createCompileUnit</span><span class="p">(</span>
+    <span class="n">dwarf</span><span class="o">::</span><span class="n">DW_LANG_C</span><span class="p">,</span> <span class="s">"fib.ks"</span><span class="p">,</span> <span class="s">"."</span><span class="p">,</span> <span class="s">"Kaleidoscope Compiler"</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="s">""</span><span class="p">,</span> <span class="mi">0</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>There are a couple of things to note here. First, while we’re producing a
+compile unit for a language called Kaleidoscope we used the language
+constant for C. This is because a debugger wouldn’t necessarily understand
+the calling conventions or default ABI for a language it doesn’t recognize
+and we follow the C ABI in our llvm code generation so it’s the closest
+thing to accurate. This ensures we can actually call functions from the
+debugger and have them execute. Secondly, you’ll see the “fib.ks” in the
+call to <tt class="docutils literal"><span class="pre">createCompileUnit</span></tt>. This is a default hard coded value since
+we’re using shell redirection to put our source into the Kaleidoscope
+compiler. In a usual front end you’d have an input file name and it would
+go there.</p>
+<p>One last thing as part of emitting debug information via DIBuilder is that
+we need to “finalize” the debug information. The reasons are part of the
+underlying API for DIBuilder, but make sure you do this near the end of
+main:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">DBuilder</span><span class="o">-></span><span class="n">finalize</span><span class="p">();</span>
+</pre></div>
+</div>
+<p>before you dump out the module.</p>
+</div>
+<div class="section" id="functions">
+<h2><a class="toc-backref" href="#id6">8.6. Functions</a><a class="headerlink" href="#functions" title="Permalink to this headline">¶</a></h2>
+<p>Now that we have our <tt class="docutils literal"><span class="pre">Compile</span> <span class="pre">Unit</span></tt> and our source locations, we can add
+function definitions to the debug info. So in <tt class="docutils literal"><span class="pre">PrototypeAST::Codegen</span></tt> we
+add a few lines of code to describe a context for our subprogram, in this
+case the “File”, and the actual definition of the function itself.</p>
+<p>So the context:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">DIFile</span> <span class="o">*</span><span class="n">Unit</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createFile</span><span class="p">(</span><span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">TheCU</span><span class="p">.</span><span class="n">getFilename</span><span class="p">(),</span>
+                                    <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">TheCU</span><span class="p">.</span><span class="n">getDirectory</span><span class="p">());</span>
+</pre></div>
+</div>
+<p>giving us an DIFile and asking the <tt class="docutils literal"><span class="pre">Compile</span> <span class="pre">Unit</span></tt> we created above for the
+directory and filename where we are currently. Then, for now, we use some
+source locations of 0 (since our AST doesn’t currently have source location
+information) and construct our function definition:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">DIScope</span> <span class="o">*</span><span class="n">FContext</span> <span class="o">=</span> <span class="n">Unit</span><span class="p">;</span>
+<span class="kt">unsigned</span> <span class="n">LineNo</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+<span class="kt">unsigned</span> <span class="n">ScopeLine</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+<span class="n">DISubprogram</span> <span class="o">*</span><span class="n">SP</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createFunction</span><span class="p">(</span>
+    <span class="n">FContext</span><span class="p">,</span> <span class="n">Name</span><span class="p">,</span> <span class="n">StringRef</span><span class="p">(),</span> <span class="n">Unit</span><span class="p">,</span> <span class="n">LineNo</span><span class="p">,</span>
+    <span class="n">CreateFunctionType</span><span class="p">(</span><span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">(),</span> <span class="n">Unit</span><span class="p">),</span> <span class="nb">false</span> <span class="cm">/* internal linkage */</span><span class="p">,</span>
+    <span class="nb">true</span> <span class="cm">/* definition */</span><span class="p">,</span> <span class="n">ScopeLine</span><span class="p">,</span> <span class="n">DINode</span><span class="o">::</span><span class="n">FlagPrototyped</span><span class="p">,</span> <span class="nb">false</span><span class="p">,</span> <span class="n">F</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>and we now have an DISubprogram that contains a reference to all of our
+metadata for the function.</p>
+</div>
+<div class="section" id="source-locations">
+<h2><a class="toc-backref" href="#id7">8.7. Source Locations</a><a class="headerlink" href="#source-locations" title="Permalink to this headline">¶</a></h2>
+<p>The most important thing for debug information is accurate source location -
+this makes it possible to map your source code back. We have a problem though,
+Kaleidoscope really doesn’t have any source location information in the lexer
+or parser so we’ll need to add it.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">struct</span> <span class="n">SourceLocation</span> <span class="p">{</span>
+  <span class="kt">int</span> <span class="n">Line</span><span class="p">;</span>
+  <span class="kt">int</span> <span class="n">Col</span><span class="p">;</span>
+<span class="p">};</span>
+<span class="k">static</span> <span class="n">SourceLocation</span> <span class="n">CurLoc</span><span class="p">;</span>
+<span class="k">static</span> <span class="n">SourceLocation</span> <span class="n">LexLoc</span> <span class="o">=</span> <span class="p">{</span><span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">};</span>
+
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">advance</span><span class="p">()</span> <span class="p">{</span>
+  <span class="kt">int</span> <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'\n'</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'\r'</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">LexLoc</span><span class="p">.</span><span class="n">Line</span><span class="o">++</span><span class="p">;</span>
+    <span class="n">LexLoc</span><span class="p">.</span><span class="n">Col</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span> <span class="k">else</span>
+    <span class="n">LexLoc</span><span class="p">.</span><span class="n">Col</span><span class="o">++</span><span class="p">;</span>
+  <span class="k">return</span> <span class="n">LastChar</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>In this set of code we’ve added some functionality on how to keep track of the
+line and column of the “source file”. As we lex every token we set our current
+current “lexical location” to the assorted line and column for the beginning
+of the token. We do this by overriding all of the previous calls to
+<tt class="docutils literal"><span class="pre">getchar()</span></tt> with our new <tt class="docutils literal"><span class="pre">advance()</span></tt> that keeps track of the information
+and then we have added to all of our AST classes a source location:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="k">class</span> <span class="nc">ExprAST</span> <span class="p">{</span>
+  <span class="n">SourceLocation</span> <span class="n">Loc</span><span class="p">;</span>
+
+  <span class="nl">public:</span>
+    <span class="kt">int</span> <span class="n">getLine</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">Loc</span><span class="p">.</span><span class="n">Line</span><span class="p">;</span> <span class="p">}</span>
+    <span class="kt">int</span> <span class="n">getCol</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">Loc</span><span class="p">.</span><span class="n">Col</span><span class="p">;</span> <span class="p">}</span>
+    <span class="n">ExprAST</span><span class="p">(</span><span class="n">SourceLocation</span> <span class="n">Loc</span> <span class="o">=</span> <span class="n">CurLoc</span><span class="p">)</span> <span class="o">:</span> <span class="n">Loc</span><span class="p">(</span><span class="n">Loc</span><span class="p">)</span> <span class="p">{}</span>
+    <span class="k">virtual</span> <span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">dump</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">out</span><span class="p">,</span> <span class="kt">int</span> <span class="n">ind</span><span class="p">)</span> <span class="p">{</span>
+      <span class="k">return</span> <span class="n">out</span> <span class="o"><<</span> <span class="sc">':'</span> <span class="o"><<</span> <span class="n">getLine</span><span class="p">()</span> <span class="o"><<</span> <span class="sc">':'</span> <span class="o"><<</span> <span class="n">getCol</span><span class="p">()</span> <span class="o"><<</span> <span class="sc">'\n'</span><span class="p">;</span>
+    <span class="p">}</span>
+</pre></div>
+</div>
+<p>that we pass down through when we create a new expression:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">LHS</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BinaryExprAST</span><span class="p">(</span><span class="n">BinLoc</span><span class="p">,</span> <span class="n">BinOp</span><span class="p">,</span> <span class="n">LHS</span><span class="p">,</span> <span class="n">RHS</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>giving us locations for each of our expressions and variables.</p>
+<p>From this we can make sure to tell <tt class="docutils literal"><span class="pre">DIBuilder</span></tt> when we’re at a new source
+location so it can use that when we generate the rest of our code and make
+sure that each instruction has source location information. We do this
+by constructing another small function:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="kt">void</span> <span class="n">DebugInfo</span><span class="o">::</span><span class="n">emitLocation</span><span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">AST</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">DIScope</span> <span class="o">*</span><span class="n">Scope</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">LexicalBlocks</span><span class="p">.</span><span class="n">empty</span><span class="p">())</span>
+    <span class="n">Scope</span> <span class="o">=</span> <span class="n">TheCU</span><span class="p">;</span>
+  <span class="k">else</span>
+    <span class="n">Scope</span> <span class="o">=</span> <span class="n">LexicalBlocks</span><span class="p">.</span><span class="n">back</span><span class="p">();</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetCurrentDebugLocation</span><span class="p">(</span>
+      <span class="n">DebugLoc</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">AST</span><span class="o">-></span><span class="n">getLine</span><span class="p">(),</span> <span class="n">AST</span><span class="o">-></span><span class="n">getCol</span><span class="p">(),</span> <span class="n">Scope</span><span class="p">));</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p>that both tells the main <tt class="docutils literal"><span class="pre">IRBuilder</span></tt> where we are, but also what scope
+we’re in. Since we’ve just created a function above we can either be in
+the main file scope (like when we created our function), or now we can be
+in the function scope we just created. To represent this we create a stack
+of scopes:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">DIScope</span> <span class="o">*></span> <span class="n">LexicalBlocks</span><span class="p">;</span>
+<span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="k">const</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="p">,</span> <span class="n">DIScope</span> <span class="o">*></span> <span class="n">FnScopeMap</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>and keep a map of each function to the scope that it represents (an
+DISubprogram is also an DIScope).</p>
+<p>Then we make sure to:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="k">this</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>emit the location every time we start to generate code for a new AST, and
+also:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">FnScopeMap</span><span class="p">[</span><span class="k">this</span><span class="p">]</span> <span class="o">=</span> <span class="n">SP</span><span class="p">;</span>
+</pre></div>
+</div>
+<p>store the scope (function) when we create it and use it:</p>
+<blockquote>
+<div>KSDbgInfo.LexicalBlocks.push_back(&KSDbgInfo.FnScopeMap[Proto]);</div></blockquote>
+<p>when we start generating the code for each function.</p>
+<p>also, don’t forget to pop the scope back off of your scope stack at the
+end of the code generation for the function:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Pop off the lexical block for the function since we added it</span>
+<span class="c1">// unconditionally.</span>
+<span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">LexicalBlocks</span><span class="p">.</span><span class="n">pop_back</span><span class="p">();</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="variables">
+<h2><a class="toc-backref" href="#id8">8.8. Variables</a><a class="headerlink" href="#variables" title="Permalink to this headline">¶</a></h2>
+<p>Now that we have functions, we need to be able to print out the variables
+we have in scope. Let’s get our function arguments set up so we can get
+decent backtraces and see how our functions are being called. It isn’t
+a lot of code, and we generally handle it when we’re creating the
+argument allocas in <tt class="docutils literal"><span class="pre">PrototypeAST::CreateArgumentAllocas</span></tt>.</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">DIScope</span> <span class="o">*</span><span class="n">Scope</span> <span class="o">=</span> <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">LexicalBlocks</span><span class="p">.</span><span class="n">back</span><span class="p">();</span>
+<span class="n">DIFile</span> <span class="o">*</span><span class="n">Unit</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createFile</span><span class="p">(</span><span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">TheCU</span><span class="p">.</span><span class="n">getFilename</span><span class="p">(),</span>
+                                    <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">TheCU</span><span class="p">.</span><span class="n">getDirectory</span><span class="p">());</span>
+<span class="n">DILocalVariable</span> <span class="n">D</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createLocalVariable</span><span class="p">(</span>
+    <span class="n">dwarf</span><span class="o">::</span><span class="n">DW_TAG_arg_variable</span><span class="p">,</span> <span class="n">Scope</span><span class="p">,</span> <span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">],</span> <span class="n">Unit</span><span class="p">,</span> <span class="n">Line</span><span class="p">,</span>
+    <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">getDoubleTy</span><span class="p">(),</span> <span class="n">Idx</span><span class="p">);</span>
+
+<span class="n">Instruction</span> <span class="o">*</span><span class="n">Call</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">insertDeclare</span><span class="p">(</span>
+    <span class="n">Alloca</span><span class="p">,</span> <span class="n">D</span><span class="p">,</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createExpression</span><span class="p">(),</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">());</span>
+<span class="n">Call</span><span class="o">-></span><span class="n">setDebugLoc</span><span class="p">(</span><span class="n">DebugLoc</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">Line</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">Scope</span><span class="p">));</span>
+</pre></div>
+</div>
+<p>Here we’re doing a few things. First, we’re grabbing our current scope
+for the variable so we can say what range of code our variable is valid
+through. Second, we’re creating the variable, giving it the scope,
+the name, source location, type, and since it’s an argument, the argument
+index. Third, we create an <tt class="docutils literal"><span class="pre">lvm.dbg.declare</span></tt> call to indicate at the IR
+level that we’ve got a variable in an alloca (and it gives a starting
+location for the variable). Lastly, we set a source location for the
+beginning of the scope on the declare.</p>
+<p>One interesting thing to note at this point is that various debuggers have
+assumptions based on how code and debug information was generated for them
+in the past. In this case we need to do a little bit of a hack to avoid
+generating line information for the function prologue so that the debugger
+knows to skip over those instructions when setting a breakpoint. So in
+<tt class="docutils literal"><span class="pre">FunctionAST::CodeGen</span></tt> we add a couple of lines:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="c1">// Unset the location for the prologue emission (leading instructions with no</span>
+<span class="c1">// location in a function are considered part of the prologue and the debugger</span>
+<span class="c1">// will run past them when breaking on a function)</span>
+<span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="n">nullptr</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>and then emit a new location when we actually start generating code for the
+body of the function:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="n">Body</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>With this we have enough debug information to set breakpoints in functions,
+print out argument variables, and call functions. Not too bad for just a
+few simple lines of code!</p>
+</div>
+<div class="section" id="full-code-listing">
+<h2><a class="toc-backref" href="#id9">8.9. Full Code Listing</a><a class="headerlink" href="#full-code-listing" title="Permalink to this headline">¶</a></h2>
+<p>Here is the complete code listing for our running example, enhanced with
+debug information. To build this example, use:</p>
+<div class="highlight-bash"><div class="highlight"><pre><span class="c"># Compile</span>
+clang++ -g toy.cpp <span class="sb">`</span>llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native<span class="sb">`</span> -O3 -o toy
+<span class="c"># Run</span>
+./toy
+</pre></div>
+</div>
+<p>Here is the code:</p>
+<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include "llvm/ADT/STLExtras.h"</span>
+<span class="cp">#include "llvm/ADT/Triple.h"</span>
+<span class="cp">#include "llvm/Analysis/Passes.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/ExecutionEngine.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/MCJIT.h"</span>
+<span class="cp">#include "llvm/ExecutionEngine/SectionMemoryManager.h"</span>
+<span class="cp">#include "llvm/IR/DIBuilder.h"</span>
+<span class="cp">#include "llvm/IR/DataLayout.h"</span>
+<span class="cp">#include "llvm/IR/DerivedTypes.h"</span>
+<span class="cp">#include "llvm/IR/IRBuilder.h"</span>
+<span class="cp">#include "llvm/IR/LLVMContext.h"</span>
+<span class="cp">#include "llvm/IR/LegacyPassManager.h"</span>
+<span class="cp">#include "llvm/IR/Module.h"</span>
+<span class="cp">#include "llvm/IR/Verifier.h"</span>
+<span class="cp">#include "llvm/Support/Host.h"</span>
+<span class="cp">#include "llvm/Support/TargetSelect.h"</span>
+<span class="cp">#include "llvm/Transforms/Scalar.h"</span>
+<span class="cp">#include <cctype></span>
+<span class="cp">#include <cstdio></span>
+<span class="cp">#include <iostream></span>
+<span class="cp">#include <map></span>
+<span class="cp">#include <string></span>
+<span class="cp">#include <vector></span>
+<span class="k">using</span> <span class="k">namespace</span> <span class="n">llvm</span><span class="p">;</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Lexer</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">// The lexer returns tokens [0-255] if it is an unknown character, otherwise one</span>
+<span class="c1">// of these for known things.</span>
+<span class="k">enum</span> <span class="n">Token</span> <span class="p">{</span>
+  <span class="n">tok_eof</span> <span class="o">=</span> <span class="o">-</span><span class="mi">1</span><span class="p">,</span>
+
+  <span class="c1">// commands</span>
+  <span class="n">tok_def</span> <span class="o">=</span> <span class="o">-</span><span class="mi">2</span><span class="p">,</span>
+  <span class="n">tok_extern</span> <span class="o">=</span> <span class="o">-</span><span class="mi">3</span><span class="p">,</span>
+
+  <span class="c1">// primary</span>
+  <span class="n">tok_identifier</span> <span class="o">=</span> <span class="o">-</span><span class="mi">4</span><span class="p">,</span>
+  <span class="n">tok_number</span> <span class="o">=</span> <span class="o">-</span><span class="mi">5</span><span class="p">,</span>
+
+  <span class="c1">// control</span>
+  <span class="n">tok_if</span> <span class="o">=</span> <span class="o">-</span><span class="mi">6</span><span class="p">,</span>
+  <span class="n">tok_then</span> <span class="o">=</span> <span class="o">-</span><span class="mi">7</span><span class="p">,</span>
+  <span class="n">tok_else</span> <span class="o">=</span> <span class="o">-</span><span class="mi">8</span><span class="p">,</span>
+  <span class="n">tok_for</span> <span class="o">=</span> <span class="o">-</span><span class="mi">9</span><span class="p">,</span>
+  <span class="n">tok_in</span> <span class="o">=</span> <span class="o">-</span><span class="mi">10</span><span class="p">,</span>
+
+  <span class="c1">// operators</span>
+  <span class="n">tok_binary</span> <span class="o">=</span> <span class="o">-</span><span class="mi">11</span><span class="p">,</span>
+  <span class="n">tok_unary</span> <span class="o">=</span> <span class="o">-</span><span class="mi">12</span><span class="p">,</span>
+
+  <span class="c1">// var definition</span>
+  <span class="n">tok_var</span> <span class="o">=</span> <span class="o">-</span><span class="mi">13</span>
+<span class="p">};</span>
+
+<span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">getTokName</span><span class="p">(</span><span class="kt">int</span> <span class="n">Tok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="k">switch</span> <span class="p">(</span><span class="n">Tok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="k">case</span> <span class="n">tok_eof</span>:
+    <span class="k">return</span> <span class="s">"eof"</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_def</span>:
+    <span class="k">return</span> <span class="s">"def"</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_extern</span>:
+    <span class="k">return</span> <span class="s">"extern"</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>:
+    <span class="k">return</span> <span class="s">"identifier"</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_number</span>:
+    <span class="k">return</span> <span class="s">"number"</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_if</span>:
+    <span class="k">return</span> <span class="s">"if"</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_then</span>:
+    <span class="k">return</span> <span class="s">"then"</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_else</span>:
+    <span class="k">return</span> <span class="s">"else"</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_for</span>:
+    <span class="k">return</span> <span class="s">"for"</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_in</span>:
+    <span class="k">return</span> <span class="s">"in"</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_binary</span>:
+    <span class="k">return</span> <span class="s">"binary"</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_unary</span>:
+    <span class="k">return</span> <span class="s">"unary"</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_var</span>:
+    <span class="k">return</span> <span class="s">"var"</span><span class="p">;</span>
+  <span class="p">}</span>
+  <span class="k">return</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="p">(</span><span class="kt">char</span><span class="p">)</span><span class="n">Tok</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="k">namespace</span> <span class="p">{</span>
+<span class="k">class</span> <span class="nc">PrototypeAST</span><span class="p">;</span>
+<span class="k">class</span> <span class="nc">ExprAST</span><span class="p">;</span>
+<span class="p">}</span>
+<span class="k">static</span> <span class="n">IRBuilder</span><span class="o"><></span> <span class="n">Builder</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">());</span>
+<span class="k">struct</span> <span class="n">DebugInfo</span> <span class="p">{</span>
+  <span class="n">DICompileUnit</span> <span class="o">*</span><span class="n">TheCU</span><span class="p">;</span>
+  <span class="n">DIType</span> <span class="o">*</span><span class="n">DblTy</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">DIScope</span> <span class="o">*></span> <span class="n">LexicalBlocks</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="k">const</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="p">,</span> <span class="n">DIScope</span> <span class="o">*></span> <span class="n">FnScopeMap</span><span class="p">;</span>
+
+  <span class="kt">void</span> <span class="nf">emitLocation</span><span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">AST</span><span class="p">);</span>
+  <span class="n">DIType</span> <span class="o">*</span><span class="nf">getDoubleTy</span><span class="p">();</span>
+<span class="p">}</span> <span class="n">KSDbgInfo</span><span class="p">;</span>
+
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdentifierStr</span><span class="p">;</span> <span class="c1">// Filled in if tok_identifier</span>
+<span class="k">static</span> <span class="kt">double</span> <span class="n">NumVal</span><span class="p">;</span>             <span class="c1">// Filled in if tok_number</span>
+<span class="k">struct</span> <span class="n">SourceLocation</span> <span class="p">{</span>
+  <span class="kt">int</span> <span class="n">Line</span><span class="p">;</span>
+  <span class="kt">int</span> <span class="n">Col</span><span class="p">;</span>
+<span class="p">};</span>
+<span class="k">static</span> <span class="n">SourceLocation</span> <span class="n">CurLoc</span><span class="p">;</span>
+<span class="k">static</span> <span class="n">SourceLocation</span> <span class="n">LexLoc</span> <span class="o">=</span> <span class="p">{</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">0</span> <span class="p">};</span>
+
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">advance</span><span class="p">()</span> <span class="p">{</span>
+  <span class="kt">int</span> <span class="n">LastChar</span> <span class="o">=</span> <span class="n">getchar</span><span class="p">();</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'\n'</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'\r'</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">LexLoc</span><span class="p">.</span><span class="n">Line</span><span class="o">++</span><span class="p">;</span>
+    <span class="n">LexLoc</span><span class="p">.</span><span class="n">Col</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span> <span class="k">else</span>
+    <span class="n">LexLoc</span><span class="p">.</span><span class="n">Col</span><span class="o">++</span><span class="p">;</span>
+  <span class="k">return</span> <span class="n">LastChar</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// gettok - Return the next token from standard input.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">gettok</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">static</span> <span class="kt">int</span> <span class="n">LastChar</span> <span class="o">=</span> <span class="sc">' '</span><span class="p">;</span>
+
+  <span class="c1">// Skip any whitespace.</span>
+  <span class="k">while</span> <span class="p">(</span><span class="n">isspace</span><span class="p">(</span><span class="n">LastChar</span><span class="p">))</span>
+    <span class="n">LastChar</span> <span class="o">=</span> <span class="n">advance</span><span class="p">();</span>
+
+  <span class="n">CurLoc</span> <span class="o">=</span> <span class="n">LexLoc</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">isalpha</span><span class="p">(</span><span class="n">LastChar</span><span class="p">))</span> <span class="p">{</span> <span class="c1">// identifier: [a-zA-Z][a-zA-Z0-9]*</span>
+    <span class="n">IdentifierStr</span> <span class="o">=</span> <span class="n">LastChar</span><span class="p">;</span>
+    <span class="k">while</span> <span class="p">(</span><span class="n">isalnum</span><span class="p">((</span><span class="n">LastChar</span> <span class="o">=</span> <span class="n">advance</span><span class="p">())))</span>
+      <span class="n">IdentifierStr</span> <span class="o">+=</span> <span class="n">LastChar</span><span class="p">;</span>
+
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"def"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_def</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"extern"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_extern</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"if"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_if</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"then"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_then</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"else"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_else</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"for"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_for</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"in"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_in</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"binary"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_binary</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"unary"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_unary</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">IdentifierStr</span> <span class="o">==</span> <span class="s">"var"</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">tok_var</span><span class="p">;</span>
+    <span class="k">return</span> <span class="n">tok_identifier</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">isdigit</span><span class="p">(</span><span class="n">LastChar</span><span class="p">)</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">)</span> <span class="p">{</span> <span class="c1">// Number: [0-9.]+</span>
+    <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">NumStr</span><span class="p">;</span>
+    <span class="k">do</span> <span class="p">{</span>
+      <span class="n">NumStr</span> <span class="o">+=</span> <span class="n">LastChar</span><span class="p">;</span>
+      <span class="n">LastChar</span> <span class="o">=</span> <span class="n">advance</span><span class="p">();</span>
+    <span class="p">}</span> <span class="k">while</span> <span class="p">(</span><span class="n">isdigit</span><span class="p">(</span><span class="n">LastChar</span><span class="p">)</span> <span class="o">||</span> <span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">);</span>
+
+    <span class="n">NumVal</span> <span class="o">=</span> <span class="n">strtod</span><span class="p">(</span><span class="n">NumStr</span><span class="p">.</span><span class="n">c_str</span><span class="p">(),</span> <span class="mi">0</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">tok_number</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="sc">'#'</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Comment until end of line.</span>
+    <span class="k">do</span>
+      <span class="n">LastChar</span> <span class="o">=</span> <span class="n">advance</span><span class="p">();</span>
+    <span class="k">while</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">!=</span> <span class="n">EOF</span> <span class="o">&&</span> <span class="n">LastChar</span> <span class="o">!=</span> <span class="sc">'\n'</span> <span class="o">&&</span> <span class="n">LastChar</span> <span class="o">!=</span> <span class="sc">'\r'</span><span class="p">);</span>
+
+    <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">!=</span> <span class="n">EOF</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">gettok</span><span class="p">();</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Check for end of file.  Don't eat the EOF.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">LastChar</span> <span class="o">==</span> <span class="n">EOF</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">tok_eof</span><span class="p">;</span>
+
+  <span class="c1">// Otherwise, just return the character as its ascii value.</span>
+  <span class="kt">int</span> <span class="n">ThisChar</span> <span class="o">=</span> <span class="n">LastChar</span><span class="p">;</span>
+  <span class="n">LastChar</span> <span class="o">=</span> <span class="n">advance</span><span class="p">();</span>
+  <span class="k">return</span> <span class="n">ThisChar</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Abstract Syntax Tree (aka Parse Tree)</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="k">namespace</span> <span class="p">{</span>
+
+<span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">indent</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">O</span><span class="p">,</span> <span class="kt">int</span> <span class="n">size</span><span class="p">)</span> <span class="p">{</span>
+  <span class="k">return</span> <span class="n">O</span> <span class="o"><<</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">(</span><span class="n">size</span><span class="p">,</span> <span class="sc">' '</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// ExprAST - Base class for all expression nodes.</span>
+<span class="k">class</span> <span class="nc">ExprAST</span> <span class="p">{</span>
+  <span class="n">SourceLocation</span> <span class="n">Loc</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="kt">int</span> <span class="n">getLine</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">Loc</span><span class="p">.</span><span class="n">Line</span><span class="p">;</span> <span class="p">}</span>
+  <span class="kt">int</span> <span class="n">getCol</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">Loc</span><span class="p">.</span><span class="n">Col</span><span class="p">;</span> <span class="p">}</span>
+  <span class="n">ExprAST</span><span class="p">(</span><span class="n">SourceLocation</span> <span class="n">Loc</span> <span class="o">=</span> <span class="n">CurLoc</span><span class="p">)</span> <span class="o">:</span> <span class="n">Loc</span><span class="p">(</span><span class="n">Loc</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="k">virtual</span> <span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">dump</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">out</span><span class="p">,</span> <span class="kt">int</span> <span class="n">ind</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">return</span> <span class="n">out</span> <span class="o"><<</span> <span class="sc">':'</span> <span class="o"><<</span> <span class="n">getLine</span><span class="p">()</span> <span class="o"><<</span> <span class="sc">':'</span> <span class="o"><<</span> <span class="n">getCol</span><span class="p">()</span> <span class="o"><<</span> <span class="sc">'\n'</span><span class="p">;</span>
+  <span class="p">}</span>
+  <span class="k">virtual</span> <span class="o">~</span><span class="n">ExprAST</span><span class="p">()</span> <span class="p">{}</span>
+  <span class="k">virtual</span> <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// NumberExprAST - Expression class for numeric literals like "1.0".</span>
+<span class="k">class</span> <span class="nc">NumberExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">double</span> <span class="n">Val</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">NumberExprAST</span><span class="p">(</span><span class="kt">double</span> <span class="n">val</span><span class="p">)</span> <span class="o">:</span> <span class="n">Val</span><span class="p">(</span><span class="n">val</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">dump</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">out</span><span class="p">,</span> <span class="kt">int</span> <span class="n">ind</span><span class="p">)</span> <span class="n">override</span> <span class="p">{</span>
+    <span class="k">return</span> <span class="n">ExprAST</span><span class="o">::</span><span class="n">dump</span><span class="p">(</span><span class="n">out</span> <span class="o"><<</span> <span class="n">Val</span><span class="p">,</span> <span class="n">ind</span><span class="p">);</span>
+  <span class="p">}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// VariableExprAST - Expression class for referencing a variable, like "a".</span>
+<span class="k">class</span> <span class="nc">VariableExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">VariableExprAST</span><span class="p">(</span><span class="n">SourceLocation</span> <span class="n">Loc</span><span class="p">,</span> <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">name</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">ExprAST</span><span class="p">(</span><span class="n">Loc</span><span class="p">),</span> <span class="n">Name</span><span class="p">(</span><span class="n">name</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">getName</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">Name</span><span class="p">;</span> <span class="p">}</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">dump</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">out</span><span class="p">,</span> <span class="kt">int</span> <span class="n">ind</span><span class="p">)</span> <span class="n">override</span> <span class="p">{</span>
+    <span class="k">return</span> <span class="n">ExprAST</span><span class="o">::</span><span class="n">dump</span><span class="p">(</span><span class="n">out</span> <span class="o"><<</span> <span class="n">Name</span><span class="p">,</span> <span class="n">ind</span><span class="p">);</span>
+  <span class="p">}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// UnaryExprAST - Expression class for a unary operator.</span>
+<span class="k">class</span> <span class="nc">UnaryExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">char</span> <span class="n">Opcode</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Operand</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">UnaryExprAST</span><span class="p">(</span><span class="kt">char</span> <span class="n">opcode</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">operand</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Opcode</span><span class="p">(</span><span class="n">opcode</span><span class="p">),</span> <span class="n">Operand</span><span class="p">(</span><span class="n">operand</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">dump</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">out</span><span class="p">,</span> <span class="kt">int</span> <span class="n">ind</span><span class="p">)</span> <span class="n">override</span> <span class="p">{</span>
+    <span class="n">ExprAST</span><span class="o">::</span><span class="n">dump</span><span class="p">(</span><span class="n">out</span> <span class="o"><<</span> <span class="s">"unary"</span> <span class="o"><<</span> <span class="n">Opcode</span><span class="p">,</span> <span class="n">ind</span><span class="p">);</span>
+    <span class="n">Operand</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">out</span><span class="p">;</span>
+  <span class="p">}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// BinaryExprAST - Expression class for a binary operator.</span>
+<span class="k">class</span> <span class="nc">BinaryExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="kt">char</span> <span class="n">Op</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span><span class="p">,</span> <span class="o">*</span><span class="n">RHS</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">BinaryExprAST</span><span class="p">(</span><span class="n">SourceLocation</span> <span class="n">Loc</span><span class="p">,</span> <span class="kt">char</span> <span class="n">op</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">lhs</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">rhs</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">ExprAST</span><span class="p">(</span><span class="n">Loc</span><span class="p">),</span> <span class="n">Op</span><span class="p">(</span><span class="n">op</span><span class="p">),</span> <span class="n">LHS</span><span class="p">(</span><span class="n">lhs</span><span class="p">),</span> <span class="n">RHS</span><span class="p">(</span><span class="n">rhs</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">dump</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">out</span><span class="p">,</span> <span class="kt">int</span> <span class="n">ind</span><span class="p">)</span> <span class="n">override</span> <span class="p">{</span>
+    <span class="n">ExprAST</span><span class="o">::</span><span class="n">dump</span><span class="p">(</span><span class="n">out</span> <span class="o"><<</span> <span class="s">"binary"</span> <span class="o"><<</span> <span class="n">Op</span><span class="p">,</span> <span class="n">ind</span><span class="p">);</span>
+    <span class="n">LHS</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="s">"LHS:"</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="n">RHS</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="s">"RHS:"</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">out</span><span class="p">;</span>
+  <span class="p">}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// CallExprAST - Expression class for function calls.</span>
+<span class="k">class</span> <span class="nc">CallExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Callee</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="n">Args</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">CallExprAST</span><span class="p">(</span><span class="n">SourceLocation</span> <span class="n">Loc</span><span class="p">,</span> <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">callee</span><span class="p">,</span>
+              <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="o">&</span><span class="n">args</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">ExprAST</span><span class="p">(</span><span class="n">Loc</span><span class="p">),</span> <span class="n">Callee</span><span class="p">(</span><span class="n">callee</span><span class="p">),</span> <span class="n">Args</span><span class="p">(</span><span class="n">args</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">dump</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">out</span><span class="p">,</span> <span class="kt">int</span> <span class="n">ind</span><span class="p">)</span> <span class="n">override</span> <span class="p">{</span>
+    <span class="n">ExprAST</span><span class="o">::</span><span class="n">dump</span><span class="p">(</span><span class="n">out</span> <span class="o"><<</span> <span class="s">"call "</span> <span class="o"><<</span> <span class="n">Callee</span><span class="p">,</span> <span class="n">ind</span><span class="p">);</span>
+    <span class="k">for</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">Arg</span> <span class="o">:</span> <span class="n">Args</span><span class="p">)</span>
+      <span class="n">Arg</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">),</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">out</span><span class="p">;</span>
+  <span class="p">}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// IfExprAST - Expression class for if/then/else.</span>
+<span class="k">class</span> <span class="nc">IfExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Cond</span><span class="p">,</span> <span class="o">*</span><span class="n">Then</span><span class="p">,</span> <span class="o">*</span><span class="n">Else</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">IfExprAST</span><span class="p">(</span><span class="n">SourceLocation</span> <span class="n">Loc</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">cond</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">then</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">_else</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">ExprAST</span><span class="p">(</span><span class="n">Loc</span><span class="p">),</span> <span class="n">Cond</span><span class="p">(</span><span class="n">cond</span><span class="p">),</span> <span class="n">Then</span><span class="p">(</span><span class="n">then</span><span class="p">),</span> <span class="n">Else</span><span class="p">(</span><span class="n">_else</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">dump</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">out</span><span class="p">,</span> <span class="kt">int</span> <span class="n">ind</span><span class="p">)</span> <span class="n">override</span> <span class="p">{</span>
+    <span class="n">ExprAST</span><span class="o">::</span><span class="n">dump</span><span class="p">(</span><span class="n">out</span> <span class="o"><<</span> <span class="s">"if"</span><span class="p">,</span> <span class="n">ind</span><span class="p">);</span>
+    <span class="n">Cond</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="s">"Cond:"</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="n">Then</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="s">"Then:"</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="n">Else</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="s">"Else:"</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">out</span><span class="p">;</span>
+  <span class="p">}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// ForExprAST - Expression class for for/in.</span>
+<span class="k">class</span> <span class="nc">ForExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">VarName</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Start</span><span class="p">,</span> <span class="o">*</span><span class="n">End</span><span class="p">,</span> <span class="o">*</span><span class="n">Step</span><span class="p">,</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">ForExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">varname</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">start</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">end</span><span class="p">,</span>
+             <span class="n">ExprAST</span> <span class="o">*</span><span class="n">step</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">VarName</span><span class="p">(</span><span class="n">varname</span><span class="p">),</span> <span class="n">Start</span><span class="p">(</span><span class="n">start</span><span class="p">),</span> <span class="n">End</span><span class="p">(</span><span class="n">end</span><span class="p">),</span> <span class="n">Step</span><span class="p">(</span><span class="n">step</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">dump</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">out</span><span class="p">,</span> <span class="kt">int</span> <span class="n">ind</span><span class="p">)</span> <span class="n">override</span> <span class="p">{</span>
+    <span class="n">ExprAST</span><span class="o">::</span><span class="n">dump</span><span class="p">(</span><span class="n">out</span> <span class="o"><<</span> <span class="s">"for"</span><span class="p">,</span> <span class="n">ind</span><span class="p">);</span>
+    <span class="n">Start</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="s">"Cond:"</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="n">End</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="s">"End:"</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="n">Step</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="s">"Step:"</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="n">Body</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="s">"Body:"</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">out</span><span class="p">;</span>
+  <span class="p">}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// VarExprAST - Expression class for var/in</span>
+<span class="k">class</span> <span class="nc">VarExprAST</span> <span class="o">:</span> <span class="k">public</span> <span class="n">ExprAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">pair</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*></span> <span class="o">></span> <span class="n">VarNames</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">VarExprAST</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">pair</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*></span> <span class="o">></span> <span class="o">&</span><span class="n">varnames</span><span class="p">,</span>
+             <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">VarNames</span><span class="p">(</span><span class="n">varnames</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">dump</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">out</span><span class="p">,</span> <span class="kt">int</span> <span class="n">ind</span><span class="p">)</span> <span class="n">override</span> <span class="p">{</span>
+    <span class="n">ExprAST</span><span class="o">::</span><span class="n">dump</span><span class="p">(</span><span class="n">out</span> <span class="o"><<</span> <span class="s">"var"</span><span class="p">,</span> <span class="n">ind</span><span class="p">);</span>
+    <span class="k">for</span> <span class="p">(</span><span class="k">const</span> <span class="k">auto</span> <span class="o">&</span><span class="n">NamedVar</span> <span class="o">:</span> <span class="n">VarNames</span><span class="p">)</span>
+      <span class="n">NamedVar</span><span class="p">.</span><span class="n">second</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="n">NamedVar</span><span class="p">.</span><span class="n">first</span> <span class="o"><<</span> <span class="sc">':'</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="n">Body</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="s">"Body:"</span><span class="p">,</span> <span class="n">ind</span> <span class="o">+</span> <span class="mi">1</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">out</span><span class="p">;</span>
+  <span class="p">}</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">()</span> <span class="n">override</span><span class="p">;</span>
+<span class="p">};</span>
+
+<span class="c1">/// PrototypeAST - This class represents the "prototype" for a function,</span>
+<span class="c1">/// which captures its argument names as well as if it is an operator.</span>
+<span class="k">class</span> <span class="nc">PrototypeAST</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span><span class="p">;</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">Args</span><span class="p">;</span>
+  <span class="kt">bool</span> <span class="n">isOperator</span><span class="p">;</span>
+  <span class="kt">unsigned</span> <span class="n">Precedence</span><span class="p">;</span> <span class="c1">// Precedence if a binary op.</span>
+  <span class="kt">int</span> <span class="n">Line</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">PrototypeAST</span><span class="p">(</span><span class="n">SourceLocation</span> <span class="n">Loc</span><span class="p">,</span> <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">name</span><span class="p">,</span>
+               <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="o">&</span><span class="n">args</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">isoperator</span> <span class="o">=</span> <span class="nb">false</span><span class="p">,</span>
+               <span class="kt">unsigned</span> <span class="n">prec</span> <span class="o">=</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="o">:</span> <span class="n">Name</span><span class="p">(</span><span class="n">name</span><span class="p">),</span> <span class="n">Args</span><span class="p">(</span><span class="n">args</span><span class="p">),</span> <span class="n">isOperator</span><span class="p">(</span><span class="n">isoperator</span><span class="p">),</span> <span class="n">Precedence</span><span class="p">(</span><span class="n">prec</span><span class="p">),</span>
+        <span class="n">Line</span><span class="p">(</span><span class="n">Loc</span><span class="p">.</span><span class="n">Line</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="kt">bool</span> <span class="n">isUnaryOp</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">isOperator</span> <span class="o">&&</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">==</span> <span class="mi">1</span><span class="p">;</span> <span class="p">}</span>
+  <span class="kt">bool</span> <span class="n">isBinaryOp</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">isOperator</span> <span class="o">&&</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">==</span> <span class="mi">2</span><span class="p">;</span> <span class="p">}</span>
+
+  <span class="kt">char</span> <span class="n">getOperatorName</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span>
+    <span class="n">assert</span><span class="p">(</span><span class="n">isUnaryOp</span><span class="p">()</span> <span class="o">||</span> <span class="n">isBinaryOp</span><span class="p">());</span>
+    <span class="k">return</span> <span class="n">Name</span><span class="p">[</span><span class="n">Name</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">-</span> <span class="mi">1</span><span class="p">];</span>
+  <span class="p">}</span>
+
+  <span class="kt">unsigned</span> <span class="n">getBinaryPrecedence</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">Precedence</span><span class="p">;</span> <span class="p">}</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+
+  <span class="kt">void</span> <span class="nf">CreateArgumentAllocas</span><span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">F</span><span class="p">);</span>
+  <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="o">&</span><span class="n">getArgs</span><span class="p">()</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">Args</span><span class="p">;</span> <span class="p">}</span>
+<span class="p">};</span>
+
+<span class="c1">/// FunctionAST - This class represents a function definition itself.</span>
+<span class="k">class</span> <span class="nc">FunctionAST</span> <span class="p">{</span>
+  <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span><span class="p">;</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span><span class="p">;</span>
+
+<span class="nl">public:</span>
+  <span class="n">FunctionAST</span><span class="p">(</span><span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">proto</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">body</span><span class="p">)</span> <span class="o">:</span> <span class="n">Proto</span><span class="p">(</span><span class="n">proto</span><span class="p">),</span> <span class="n">Body</span><span class="p">(</span><span class="n">body</span><span class="p">)</span> <span class="p">{}</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">dump</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">ostream</span> <span class="o">&</span><span class="n">out</span><span class="p">,</span> <span class="kt">int</span> <span class="n">ind</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="s">"FunctionAST</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span>
+    <span class="o">++</span><span class="n">ind</span><span class="p">;</span>
+    <span class="n">indent</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o"><<</span> <span class="s">"Body:"</span><span class="p">;</span>
+    <span class="k">return</span> <span class="n">Body</span> <span class="o">?</span> <span class="n">Body</span><span class="o">-></span><span class="n">dump</span><span class="p">(</span><span class="n">out</span><span class="p">,</span> <span class="n">ind</span><span class="p">)</span> <span class="o">:</span> <span class="n">out</span> <span class="o"><<</span> <span class="s">"null</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">Codegen</span><span class="p">();</span>
+<span class="p">};</span>
+<span class="p">}</span> <span class="c1">// end anonymous namespace</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Parser</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">/// CurTok/getNextToken - Provide a simple token buffer.  CurTok is the current</span>
+<span class="c1">/// token the parser is looking at.  getNextToken reads another token from the</span>
+<span class="c1">/// lexer and updates CurTok with its results.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="n">CurTok</span><span class="p">;</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">getNextToken</span><span class="p">()</span> <span class="p">{</span> <span class="k">return</span> <span class="n">CurTok</span> <span class="o">=</span> <span class="n">gettok</span><span class="p">();</span> <span class="p">}</span>
+
+<span class="c1">/// BinopPrecedence - This holds the precedence for each binary operator that is</span>
+<span class="c1">/// defined.</span>
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="kt">char</span><span class="p">,</span> <span class="kt">int</span><span class="o">></span> <span class="n">BinopPrecedence</span><span class="p">;</span>
+
+<span class="c1">/// GetTokPrecedence - Get the precedence of the pending binary operator token.</span>
+<span class="k">static</span> <span class="kt">int</span> <span class="nf">GetTokPrecedence</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+    <span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
+
+  <span class="c1">// Make sure it's a declared binop.</span>
+  <span class="kt">int</span> <span class="n">TokPrec</span> <span class="o">=</span> <span class="n">BinopPrecedence</span><span class="p">[</span><span class="n">CurTok</span><span class="p">];</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><=</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="o">-</span><span class="mi">1</span><span class="p">;</span>
+  <span class="k">return</span> <span class="n">TokPrec</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// Error* - These are little helper functions for error handling.</span>
+<span class="n">ExprAST</span> <span class="o">*</span><span class="nf">Error</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Error: %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+<span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ErrorP</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+<span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ErrorF</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseExpression</span><span class="p">();</span>
+
+<span class="c1">/// identifierexpr</span>
+<span class="c1">///   ::= identifier</span>
+<span class="c1">///   ::= identifier '(' expression* ')'</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseIdentifierExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+
+  <span class="n">SourceLocation</span> <span class="n">LitLoc</span> <span class="o">=</span> <span class="n">CurLoc</span><span class="p">;</span>
+
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat identifier.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'('</span><span class="p">)</span> <span class="c1">// Simple variable ref.</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">VariableExprAST</span><span class="p">(</span><span class="n">LitLoc</span><span class="p">,</span> <span class="n">IdName</span><span class="p">);</span>
+
+  <span class="c1">// Call.</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat (</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">ExprAST</span> <span class="o">*></span> <span class="n">Args</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Arg</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+      <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Arg</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+      <span class="n">Args</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">Arg</span><span class="p">);</span>
+
+      <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">')'</span><span class="p">)</span>
+        <span class="k">break</span><span class="p">;</span>
+
+      <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span>
+        <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"Expected ')' or ',' in argument list"</span><span class="p">);</span>
+      <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Eat the ')'.</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">CallExprAST</span><span class="p">(</span><span class="n">LitLoc</span><span class="p">,</span> <span class="n">IdName</span><span class="p">,</span> <span class="n">Args</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// numberexpr ::= number</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseNumberExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Result</span> <span class="o">=</span> <span class="k">new</span> <span class="n">NumberExprAST</span><span class="p">(</span><span class="n">NumVal</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// consume the number</span>
+  <span class="k">return</span> <span class="n">Result</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// parenexpr ::= '(' expression ')'</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseParenExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat (.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">V</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">V</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected ')'"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat ).</span>
+  <span class="k">return</span> <span class="n">V</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// ifexpr ::= 'if' expression 'then' expression 'else' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseIfExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">SourceLocation</span> <span class="n">IfLoc</span> <span class="o">=</span> <span class="n">CurLoc</span><span class="p">;</span>
+
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the if.</span>
+
+  <span class="c1">// condition.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Cond</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Cond</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_then</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected then"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the then</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Then</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Then</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_else</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected else"</span><span class="p">);</span>
+
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Else</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Else</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">IfExprAST</span><span class="p">(</span><span class="n">IfLoc</span><span class="p">,</span> <span class="n">Cond</span><span class="p">,</span> <span class="n">Then</span><span class="p">,</span> <span class="n">Else</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseForExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the for.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected identifier after for"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">IdName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat identifier.</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'='</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected '=' after for"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat '='.</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Start</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Start</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected ',' after for start value"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">End</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">End</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// The step value is optional.</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Step</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">','</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="n">Step</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Step</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_in</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected 'in' after for"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat 'in'.</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Body</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">ForExprAST</span><span class="p">(</span><span class="n">IdName</span><span class="p">,</span> <span class="n">Start</span><span class="p">,</span> <span class="n">End</span><span class="p">,</span> <span class="n">Step</span><span class="p">,</span> <span class="n">Body</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// varexpr ::= 'var' identifier ('=' expression)?</span>
+<span class="c1">//                    (',' identifier ('=' expression)?)* 'in' expression</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseVarExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the var.</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">pair</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*></span> <span class="o">></span> <span class="n">VarNames</span><span class="p">;</span>
+
+  <span class="c1">// At least one variable name is required.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected identifier after var"</span><span class="p">);</span>
+
+  <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">Name</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat identifier.</span>
+
+    <span class="c1">// Read the optional initializer.</span>
+    <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Init</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="sc">'='</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the '='.</span>
+
+      <span class="n">Init</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">Init</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+
+    <span class="n">VarNames</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">make_pair</span><span class="p">(</span><span class="n">Name</span><span class="p">,</span> <span class="n">Init</span><span class="p">));</span>
+
+    <span class="c1">// End of var list, exit loop.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">','</span><span class="p">)</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat the ','.</span>
+
+    <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_identifier</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected identifier list after var"</span><span class="p">);</span>
+  <span class="p">}</span>
+
+  <span class="c1">// At this point, we have to have 'in'.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="n">tok_in</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"expected 'in' keyword after 'var'"</span><span class="p">);</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat 'in'.</span>
+
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Body</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Body</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">VarExprAST</span><span class="p">(</span><span class="n">VarNames</span><span class="p">,</span> <span class="n">Body</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// primary</span>
+<span class="c1">///   ::= identifierexpr</span>
+<span class="c1">///   ::= numberexpr</span>
+<span class="c1">///   ::= parenexpr</span>
+<span class="c1">///   ::= ifexpr</span>
+<span class="c1">///   ::= forexpr</span>
+<span class="c1">///   ::= varexpr</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParsePrimary</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="nl">default:</span>
+    <span class="k">return</span> <span class="n">Error</span><span class="p">(</span><span class="s">"unknown token when expecting an expression"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>:
+    <span class="k">return</span> <span class="n">ParseIdentifierExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_number</span>:
+    <span class="k">return</span> <span class="n">ParseNumberExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="sc">'('</span>:
+    <span class="k">return</span> <span class="n">ParseParenExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_if</span>:
+    <span class="k">return</span> <span class="n">ParseIfExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_for</span>:
+    <span class="k">return</span> <span class="n">ParseForExpr</span><span class="p">();</span>
+  <span class="k">case</span> <span class="n">tok_var</span>:
+    <span class="k">return</span> <span class="n">ParseVarExpr</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// unary</span>
+<span class="c1">///   ::= primary</span>
+<span class="c1">///   ::= '!' unary</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseUnary</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// If the current token is not an operator, it must be a primary expr.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="o">||</span> <span class="n">CurTok</span> <span class="o">==</span> <span class="sc">'('</span> <span class="o">||</span> <span class="n">CurTok</span> <span class="o">==</span> <span class="sc">','</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ParsePrimary</span><span class="p">();</span>
+
+  <span class="c1">// If this is a unary operator, read it.</span>
+  <span class="kt">int</span> <span class="n">Opc</span> <span class="o">=</span> <span class="n">CurTok</span><span class="p">;</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">Operand</span> <span class="o">=</span> <span class="n">ParseUnary</span><span class="p">())</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">UnaryExprAST</span><span class="p">(</span><span class="n">Opc</span><span class="p">,</span> <span class="n">Operand</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// binoprhs</span>
+<span class="c1">///   ::= ('+' unary)*</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseBinOpRHS</span><span class="p">(</span><span class="kt">int</span> <span class="n">ExprPrec</span><span class="p">,</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span><span class="p">)</span> <span class="p">{</span>
+  <span class="c1">// If this is a binop, find its precedence.</span>
+  <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+    <span class="kt">int</span> <span class="n">TokPrec</span> <span class="o">=</span> <span class="n">GetTokPrecedence</span><span class="p">();</span>
+
+    <span class="c1">// If this is a binop that binds at least as tightly as the current binop,</span>
+    <span class="c1">// consume it, otherwise we are done.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><</span> <span class="n">ExprPrec</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">LHS</span><span class="p">;</span>
+
+    <span class="c1">// Okay, we know this is a binop.</span>
+    <span class="kt">int</span> <span class="n">BinOp</span> <span class="o">=</span> <span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">SourceLocation</span> <span class="n">BinLoc</span> <span class="o">=</span> <span class="n">CurLoc</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat binop</span>
+
+    <span class="c1">// Parse the unary expression after the binary operator.</span>
+    <span class="n">ExprAST</span> <span class="o">*</span><span class="n">RHS</span> <span class="o">=</span> <span class="n">ParseUnary</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">RHS</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+    <span class="c1">// If BinOp binds less tightly with RHS than the operator after RHS, let</span>
+    <span class="c1">// the pending operator take RHS as its LHS.</span>
+    <span class="kt">int</span> <span class="n">NextPrec</span> <span class="o">=</span> <span class="n">GetTokPrecedence</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">TokPrec</span> <span class="o"><</span> <span class="n">NextPrec</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">RHS</span> <span class="o">=</span> <span class="n">ParseBinOpRHS</span><span class="p">(</span><span class="n">TokPrec</span> <span class="o">+</span> <span class="mi">1</span><span class="p">,</span> <span class="n">RHS</span><span class="p">);</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">RHS</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+
+    <span class="c1">// Merge LHS/RHS.</span>
+    <span class="n">LHS</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BinaryExprAST</span><span class="p">(</span><span class="n">BinLoc</span><span class="p">,</span> <span class="n">BinOp</span><span class="p">,</span> <span class="n">LHS</span><span class="p">,</span> <span class="n">RHS</span><span class="p">);</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// expression</span>
+<span class="c1">///   ::= unary binoprhs</span>
+<span class="c1">///</span>
+<span class="k">static</span> <span class="n">ExprAST</span> <span class="o">*</span><span class="nf">ParseExpression</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">ExprAST</span> <span class="o">*</span><span class="n">LHS</span> <span class="o">=</span> <span class="n">ParseUnary</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">LHS</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">return</span> <span class="n">ParseBinOpRHS</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">LHS</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// prototype</span>
+<span class="c1">///   ::= id '(' id* ')'</span>
+<span class="c1">///   ::= binary LETTER number? (id, id)</span>
+<span class="c1">///   ::= unary LETTER (id)</span>
+<span class="k">static</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ParsePrototype</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">FnName</span><span class="p">;</span>
+
+  <span class="n">SourceLocation</span> <span class="n">FnLoc</span> <span class="o">=</span> <span class="n">CurLoc</span><span class="p">;</span>
+
+  <span class="kt">unsigned</span> <span class="n">Kind</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="c1">// 0 = identifier, 1 = unary, 2 = binary.</span>
+  <span class="kt">unsigned</span> <span class="n">BinaryPrecedence</span> <span class="o">=</span> <span class="mi">30</span><span class="p">;</span>
+
+  <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+  <span class="nl">default:</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected function name in prototype"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="n">tok_identifier</span>:
+    <span class="n">FnName</span> <span class="o">=</span> <span class="n">IdentifierStr</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_unary</span>:
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+      <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected unary operator"</span><span class="p">);</span>
+    <span class="n">FnName</span> <span class="o">=</span> <span class="s">"unary"</span><span class="p">;</span>
+    <span class="n">FnName</span> <span class="o">+=</span> <span class="p">(</span><span class="kt">char</span><span class="p">)</span><span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="k">case</span> <span class="n">tok_binary</span>:
+    <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">isascii</span><span class="p">(</span><span class="n">CurTok</span><span class="p">))</span>
+      <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected binary operator"</span><span class="p">);</span>
+    <span class="n">FnName</span> <span class="o">=</span> <span class="s">"binary"</span><span class="p">;</span>
+    <span class="n">FnName</span> <span class="o">+=</span> <span class="p">(</span><span class="kt">char</span><span class="p">)</span><span class="n">CurTok</span><span class="p">;</span>
+    <span class="n">Kind</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+
+    <span class="c1">// Read the precedence if present.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">==</span> <span class="n">tok_number</span><span class="p">)</span> <span class="p">{</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">NumVal</span> <span class="o"><</span> <span class="mi">1</span> <span class="o">||</span> <span class="n">NumVal</span> <span class="o">></span> <span class="mi">100</span><span class="p">)</span>
+        <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Invalid precedecnce: must be 1..100"</span><span class="p">);</span>
+      <span class="n">BinaryPrecedence</span> <span class="o">=</span> <span class="p">(</span><span class="kt">unsigned</span><span class="p">)</span><span class="n">NumVal</span><span class="p">;</span>
+      <span class="n">getNextToken</span><span class="p">();</span>
+    <span class="p">}</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">'('</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected '(' in prototype"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">ArgNames</span><span class="p">;</span>
+  <span class="k">while</span> <span class="p">(</span><span class="n">getNextToken</span><span class="p">()</span> <span class="o">==</span> <span class="n">tok_identifier</span><span class="p">)</span>
+    <span class="n">ArgNames</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">IdentifierStr</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CurTok</span> <span class="o">!=</span> <span class="sc">')'</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Expected ')' in prototype"</span><span class="p">);</span>
+
+  <span class="c1">// success.</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat ')'.</span>
+
+  <span class="c1">// Verify right number of names for operator.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Kind</span> <span class="o">&&</span> <span class="n">ArgNames</span><span class="p">.</span><span class="n">size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Kind</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorP</span><span class="p">(</span><span class="s">"Invalid number of operands for operator"</span><span class="p">);</span>
+
+  <span class="k">return</span> <span class="k">new</span> <span class="n">PrototypeAST</span><span class="p">(</span><span class="n">FnLoc</span><span class="p">,</span> <span class="n">FnName</span><span class="p">,</span> <span class="n">ArgNames</span><span class="p">,</span> <span class="n">Kind</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">BinaryPrecedence</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="c1">/// definition ::= 'def' prototype expression</span>
+<span class="k">static</span> <span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ParseDefinition</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat def.</span>
+  <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span> <span class="o">=</span> <span class="n">ParsePrototype</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Proto</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">E</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">())</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">FunctionAST</span><span class="p">(</span><span class="n">Proto</span><span class="p">,</span> <span class="n">E</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// toplevelexpr ::= expression</span>
+<span class="k">static</span> <span class="n">FunctionAST</span> <span class="o">*</span><span class="nf">ParseTopLevelExpr</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">SourceLocation</span> <span class="n">FnLoc</span> <span class="o">=</span> <span class="n">CurLoc</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">E</span> <span class="o">=</span> <span class="n">ParseExpression</span><span class="p">())</span> <span class="p">{</span>
+    <span class="c1">// Make an anonymous proto.</span>
+    <span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">Proto</span> <span class="o">=</span>
+        <span class="k">new</span> <span class="n">PrototypeAST</span><span class="p">(</span><span class="n">FnLoc</span><span class="p">,</span> <span class="s">"main"</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="p">());</span>
+    <span class="k">return</span> <span class="k">new</span> <span class="n">FunctionAST</span><span class="p">(</span><span class="n">Proto</span><span class="p">,</span> <span class="n">E</span><span class="p">);</span>
+  <span class="p">}</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// external ::= 'extern' prototype</span>
+<span class="k">static</span> <span class="n">PrototypeAST</span> <span class="o">*</span><span class="nf">ParseExtern</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">getNextToken</span><span class="p">();</span> <span class="c1">// eat extern.</span>
+  <span class="k">return</span> <span class="n">ParsePrototype</span><span class="p">();</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Debug Info Support</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="k">static</span> <span class="n">DIBuilder</span> <span class="o">*</span><span class="n">DBuilder</span><span class="p">;</span>
+
+<span class="n">DIType</span> <span class="o">*</span><span class="n">DebugInfo</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">DblTy</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">DblTy</span><span class="p">;</span>
+
+  <span class="n">DblTy</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createBasicType</span><span class="p">(</span><span class="s">"double"</span><span class="p">,</span> <span class="mi">64</span><span class="p">,</span> <span class="mi">64</span><span class="p">,</span> <span class="n">dwarf</span><span class="o">::</span><span class="n">DW_ATE_float</span><span class="p">);</span>
+  <span class="k">return</span> <span class="n">DblTy</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="kt">void</span> <span class="n">DebugInfo</span><span class="o">::</span><span class="n">emitLocation</span><span class="p">(</span><span class="n">ExprAST</span> <span class="o">*</span><span class="n">AST</span><span class="p">)</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">AST</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">SetCurrentDebugLocation</span><span class="p">(</span><span class="n">DebugLoc</span><span class="p">());</span>
+  <span class="n">DIScope</span> <span class="o">*</span><span class="n">Scope</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">LexicalBlocks</span><span class="p">.</span><span class="n">empty</span><span class="p">())</span>
+    <span class="n">Scope</span> <span class="o">=</span> <span class="n">TheCU</span><span class="p">;</span>
+  <span class="k">else</span>
+    <span class="n">Scope</span> <span class="o">=</span> <span class="n">LexicalBlocks</span><span class="p">.</span><span class="n">back</span><span class="p">();</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetCurrentDebugLocation</span><span class="p">(</span>
+      <span class="n">DebugLoc</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">AST</span><span class="o">-></span><span class="n">getLine</span><span class="p">(),</span> <span class="n">AST</span><span class="o">-></span><span class="n">getCol</span><span class="p">(),</span> <span class="n">Scope</span><span class="p">));</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="n">DISubroutineType</span> <span class="o">*</span><span class="n">CreateFunctionType</span><span class="p">(</span><span class="kt">unsigned</span> <span class="n">NumArgs</span><span class="p">,</span> <span class="n">DIFile</span> <span class="o">*</span><span class="n">Unit</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">SmallVector</span><span class="o"><</span><span class="n">Metadata</span> <span class="o">*</span><span class="p">,</span> <span class="mi">8</span><span class="o">></span> <span class="n">EltTys</span><span class="p">;</span>
+  <span class="n">DIType</span> <span class="o">*</span><span class="n">DblTy</span> <span class="o">=</span> <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">getDoubleTy</span><span class="p">();</span>
+
+  <span class="c1">// Add the result type.</span>
+  <span class="n">EltTys</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">DblTy</span><span class="p">);</span>
+
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">NumArgs</span><span class="p">;</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span>
+    <span class="n">EltTys</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">DblTy</span><span class="p">);</span>
+
+  <span class="k">return</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createSubroutineType</span><span class="p">(</span><span class="n">Unit</span><span class="p">,</span>
+                                        <span class="n">DBuilder</span><span class="o">-></span><span class="n">getOrCreateTypeArray</span><span class="p">(</span><span class="n">EltTys</span><span class="p">));</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Code Generation</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="k">static</span> <span class="n">Module</span> <span class="o">*</span><span class="n">TheModule</span><span class="p">;</span>
+<span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">map</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">AllocaInst</span> <span class="o">*></span> <span class="n">NamedValues</span><span class="p">;</span>
+<span class="k">static</span> <span class="n">legacy</span><span class="o">::</span><span class="n">FunctionPassManager</span> <span class="o">*</span><span class="n">TheFPM</span><span class="p">;</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="nf">ErrorV</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">Str</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Error</span><span class="p">(</span><span class="n">Str</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of</span>
+<span class="c1">/// the function.  This is used for mutable variables etc.</span>
+<span class="k">static</span> <span class="n">AllocaInst</span> <span class="o">*</span><span class="nf">CreateEntryBlockAlloca</span><span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span><span class="p">,</span>
+                                          <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">VarName</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">IRBuilder</span><span class="o"><></span> <span class="n">TmpB</span><span class="p">(</span><span class="o">&</span><span class="n">TheFunction</span><span class="o">-></span><span class="n">getEntryBlock</span><span class="p">(),</span>
+                   <span class="n">TheFunction</span><span class="o">-></span><span class="n">getEntryBlock</span><span class="p">().</span><span class="n">begin</span><span class="p">());</span>
+  <span class="k">return</span> <span class="n">TmpB</span><span class="p">.</span><span class="n">CreateAlloca</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="mi">0</span><span class="p">,</span>
+                           <span class="n">VarName</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">NumberExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="k">this</span><span class="p">);</span>
+  <span class="k">return</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="n">Val</span><span class="p">));</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">VariableExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Look this variable up in the function.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">V</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">Name</span><span class="p">];</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">V</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown variable name"</span><span class="p">);</span>
+
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="k">this</span><span class="p">);</span>
+  <span class="c1">// Load the value.</span>
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateLoad</span><span class="p">(</span><span class="n">V</span><span class="p">,</span> <span class="n">Name</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">UnaryExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">OperandV</span> <span class="o">=</span> <span class="n">Operand</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">OperandV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">(</span><span class="s">"unary"</span><span class="p">)</span> <span class="o">+</span> <span class="n">Opcode</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">F</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown unary operator"</span><span class="p">);</span>
+
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="k">this</span><span class="p">);</span>
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">F</span><span class="p">,</span> <span class="n">OperandV</span><span class="p">,</span> <span class="s">"unop"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">BinaryExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="k">this</span><span class="p">);</span>
+
+  <span class="c1">// Special case '=' because we don't want to emit the LHS as an expression.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Op</span> <span class="o">==</span> <span class="sc">'='</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Assignment requires the LHS to be an identifier.</span>
+    <span class="c1">// This assume we're building without RTTI because LLVM builds that way by</span>
+    <span class="c1">// default.  If you build LLVM with RTTI this can be changed to a</span>
+    <span class="c1">// dynamic_cast for automatic error checking.</span>
+    <span class="n">VariableExprAST</span> <span class="o">*</span><span class="n">LHSE</span> <span class="o">=</span> <span class="k">static_cast</span><span class="o"><</span><span class="n">VariableExprAST</span> <span class="o">*></span><span class="p">(</span><span class="n">LHS</span><span class="p">);</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">LHSE</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"destination of '=' must be a variable"</span><span class="p">);</span>
+    <span class="c1">// Codegen the RHS.</span>
+    <span class="n">Value</span> <span class="o">*</span><span class="n">Val</span> <span class="o">=</span> <span class="n">RHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Val</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+    <span class="c1">// Look up the name.</span>
+    <span class="n">Value</span> <span class="o">*</span><span class="n">Variable</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">LHSE</span><span class="o">-></span><span class="n">getName</span><span class="p">()];</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Variable</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown variable name"</span><span class="p">);</span>
+
+    <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">Val</span><span class="p">,</span> <span class="n">Variable</span><span class="p">);</span>
+    <span class="k">return</span> <span class="n">Val</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">L</span> <span class="o">=</span> <span class="n">LHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">R</span> <span class="o">=</span> <span class="n">RHS</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">L</span> <span class="o">==</span> <span class="mi">0</span> <span class="o">||</span> <span class="n">R</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="k">switch</span> <span class="p">(</span><span class="n">Op</span><span class="p">)</span> <span class="p">{</span>
+  <span class="k">case</span> <span class="sc">'+'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFAdd</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"addtmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'-'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFSub</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"subtmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'*'</span>:
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFMul</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"multmp"</span><span class="p">);</span>
+  <span class="k">case</span> <span class="sc">'<'</span>:
+    <span class="n">L</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpULT</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">R</span><span class="p">,</span> <span class="s">"cmptmp"</span><span class="p">);</span>
+    <span class="c1">// Convert bool 0/1 to double 0.0 or 1.0</span>
+    <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateUIToFP</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span>
+                                <span class="s">"booltmp"</span><span class="p">);</span>
+  <span class="nl">default:</span>
+    <span class="k">break</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="c1">// If it wasn't a builtin binary operator, it must be a user defined one. Emit</span>
+  <span class="c1">// a call to it.</span>
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">(</span><span class="s">"binary"</span><span class="p">)</span> <span class="o">+</span> <span class="n">Op</span><span class="p">);</span>
+  <span class="n">assert</span><span class="p">(</span><span class="n">F</span> <span class="o">&&</span> <span class="s">"binary operator not found!"</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">Ops</span><span class="p">[]</span> <span class="o">=</span> <span class="p">{</span> <span class="n">L</span><span class="p">,</span> <span class="n">R</span> <span class="p">};</span>
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">F</span><span class="p">,</span> <span class="n">Ops</span><span class="p">,</span> <span class="s">"binop"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">CallExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="k">this</span><span class="p">);</span>
+
+  <span class="c1">// Look up the name in the global module table.</span>
+  <span class="n">Function</span> <span class="o">*</span><span class="n">CalleeF</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">Callee</span><span class="p">);</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CalleeF</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Unknown function referenced"</span><span class="p">);</span>
+
+  <span class="c1">// If argument mismatch error.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CalleeF</span><span class="o">-></span><span class="n">arg_size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">())</span>
+    <span class="k">return</span> <span class="n">ErrorV</span><span class="p">(</span><span class="s">"Incorrect # arguments passed"</span><span class="p">);</span>
+
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">Value</span> <span class="o">*></span> <span class="n">ArgsV</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">ArgsV</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">Args</span><span class="p">[</span><span class="n">i</span><span class="p">]</span><span class="o">-></span><span class="n">Codegen</span><span class="p">());</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">ArgsV</span><span class="p">.</span><span class="n">back</span><span class="p">()</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="k">return</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCall</span><span class="p">(</span><span class="n">CalleeF</span><span class="p">,</span> <span class="n">ArgsV</span><span class="p">,</span> <span class="s">"calltmp"</span><span class="p">);</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">IfExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="k">this</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">CondV</span> <span class="o">=</span> <span class="n">Cond</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">CondV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Convert condition to a bool by comparing equal to 0.0.</span>
+  <span class="n">CondV</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpONE</span><span class="p">(</span>
+      <span class="n">CondV</span><span class="p">,</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">)),</span> <span class="s">"ifcond"</span><span class="p">);</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+
+  <span class="c1">// Create blocks for the then and else cases.  Insert the 'then' block at the</span>
+  <span class="c1">// end of the function.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">ThenBB</span> <span class="o">=</span>
+      <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"then"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">ElseBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"else"</span><span class="p">);</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">MergeBB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"ifcont"</span><span class="p">);</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCondBr</span><span class="p">(</span><span class="n">CondV</span><span class="p">,</span> <span class="n">ThenBB</span><span class="p">,</span> <span class="n">ElseBB</span><span class="p">);</span>
+
+  <span class="c1">// Emit then value.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">ThenBB</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">ThenV</span> <span class="o">=</span> <span class="n">Then</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ThenV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="c1">// Codegen of 'Then' can change the current block, update ThenBB for the PHI.</span>
+  <span class="n">ThenBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+
+  <span class="c1">// Emit else block.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">getBasicBlockList</span><span class="p">().</span><span class="n">push_back</span><span class="p">(</span><span class="n">ElseBB</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">ElseBB</span><span class="p">);</span>
+
+  <span class="n">Value</span> <span class="o">*</span><span class="n">ElseV</span> <span class="o">=</span> <span class="n">Else</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">ElseV</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="c1">// Codegen of 'Else' can change the current block, update ElseBB for the PHI.</span>
+  <span class="n">ElseBB</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">();</span>
+
+  <span class="c1">// Emit merge block.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">getBasicBlockList</span><span class="p">().</span><span class="n">push_back</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">MergeBB</span><span class="p">);</span>
+  <span class="n">PHINode</span> <span class="o">*</span><span class="n">PN</span> <span class="o">=</span>
+      <span class="n">Builder</span><span class="p">.</span><span class="n">CreatePHI</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="mi">2</span><span class="p">,</span> <span class="s">"iftmp"</span><span class="p">);</span>
+
+  <span class="n">PN</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">ThenV</span><span class="p">,</span> <span class="n">ThenBB</span><span class="p">);</span>
+  <span class="n">PN</span><span class="o">-></span><span class="n">addIncoming</span><span class="p">(</span><span class="n">ElseV</span><span class="p">,</span> <span class="n">ElseBB</span><span class="p">);</span>
+  <span class="k">return</span> <span class="n">PN</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">ForExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Output this as:</span>
+  <span class="c1">//   var = alloca double</span>
+  <span class="c1">//   ...</span>
+  <span class="c1">//   start = startexpr</span>
+  <span class="c1">//   store start -> var</span>
+  <span class="c1">//   goto loop</span>
+  <span class="c1">// loop:</span>
+  <span class="c1">//   ...</span>
+  <span class="c1">//   bodyexpr</span>
+  <span class="c1">//   ...</span>
+  <span class="c1">// loopend:</span>
+  <span class="c1">//   step = stepexpr</span>
+  <span class="c1">//   endcond = endexpr</span>
+  <span class="c1">//</span>
+  <span class="c1">//   curvar = load var</span>
+  <span class="c1">//   nextvar = curvar + step</span>
+  <span class="c1">//   store nextvar -> var</span>
+  <span class="c1">//   br endcond, loop, endloop</span>
+  <span class="c1">// outloop:</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+
+  <span class="c1">// Create an alloca for the variable in the entry block.</span>
+  <span class="n">AllocaInst</span> <span class="o">*</span><span class="n">Alloca</span> <span class="o">=</span> <span class="n">CreateEntryBlockAlloca</span><span class="p">(</span><span class="n">TheFunction</span><span class="p">,</span> <span class="n">VarName</span><span class="p">);</span>
+
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="k">this</span><span class="p">);</span>
+
+  <span class="c1">// Emit the start code first, without 'variable' in scope.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">StartVal</span> <span class="o">=</span> <span class="n">Start</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">StartVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Store the value into the alloca.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">StartVal</span><span class="p">,</span> <span class="n">Alloca</span><span class="p">);</span>
+
+  <span class="c1">// Make the new basic block for the loop header, inserting after current</span>
+  <span class="c1">// block.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">LoopBB</span> <span class="o">=</span>
+      <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"loop"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+
+  <span class="c1">// Insert an explicit fall through from the current block to the LoopBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateBr</span><span class="p">(</span><span class="n">LoopBB</span><span class="p">);</span>
+
+  <span class="c1">// Start insertion in LoopBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">LoopBB</span><span class="p">);</span>
+
+  <span class="c1">// Within the loop, the variable is defined equal to the PHI node.  If it</span>
+  <span class="c1">// shadows an existing variable, we have to restore it, so save it now.</span>
+  <span class="n">AllocaInst</span> <span class="o">*</span><span class="n">OldVal</span> <span class="o">=</span> <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">];</span>
+  <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">Alloca</span><span class="p">;</span>
+
+  <span class="c1">// Emit the body of the loop.  This, like any other expr, can change the</span>
+  <span class="c1">// current BB.  Note that we ignore the value computed by the body, but don't</span>
+  <span class="c1">// allow an error.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">()</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Emit the step value.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">StepVal</span><span class="p">;</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Step</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">StepVal</span> <span class="o">=</span> <span class="n">Step</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">StepVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// If not specified, use 1.0.</span>
+    <span class="n">StepVal</span> <span class="o">=</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">1.0</span><span class="p">));</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Compute the end condition.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">EndCond</span> <span class="o">=</span> <span class="n">End</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">EndCond</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="n">EndCond</span><span class="p">;</span>
+
+  <span class="c1">// Reload, increment, and restore the alloca.  This handles the case where</span>
+  <span class="c1">// the body of the loop mutates the variable.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">CurVar</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateLoad</span><span class="p">(</span><span class="n">Alloca</span><span class="p">,</span> <span class="n">VarName</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">NextVar</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFAdd</span><span class="p">(</span><span class="n">CurVar</span><span class="p">,</span> <span class="n">StepVal</span><span class="p">,</span> <span class="s">"nextvar"</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">NextVar</span><span class="p">,</span> <span class="n">Alloca</span><span class="p">);</span>
+
+  <span class="c1">// Convert condition to a bool by comparing equal to 0.0.</span>
+  <span class="n">EndCond</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">CreateFCmpONE</span><span class="p">(</span>
+      <span class="n">EndCond</span><span class="p">,</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">)),</span> <span class="s">"loopcond"</span><span class="p">);</span>
+
+  <span class="c1">// Create the "after loop" block and insert it.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">AfterBB</span> <span class="o">=</span>
+      <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"afterloop"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+
+  <span class="c1">// Insert the conditional branch into the end of LoopEndBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">CreateCondBr</span><span class="p">(</span><span class="n">EndCond</span><span class="p">,</span> <span class="n">LoopBB</span><span class="p">,</span> <span class="n">AfterBB</span><span class="p">);</span>
+
+  <span class="c1">// Any new code will be inserted in AfterBB.</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">AfterBB</span><span class="p">);</span>
+
+  <span class="c1">// Restore the unshadowed variable.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">OldVal</span><span class="p">)</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">OldVal</span><span class="p">;</span>
+  <span class="k">else</span>
+    <span class="n">NamedValues</span><span class="p">.</span><span class="n">erase</span><span class="p">(</span><span class="n">VarName</span><span class="p">);</span>
+
+  <span class="c1">// for expr always returns 0.0.</span>
+  <span class="k">return</span> <span class="n">Constant</span><span class="o">::</span><span class="n">getNullValue</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()));</span>
+<span class="p">}</span>
+
+<span class="n">Value</span> <span class="o">*</span><span class="n">VarExprAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">AllocaInst</span> <span class="o">*></span> <span class="n">OldBindings</span><span class="p">;</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">()</span><span class="o">-></span><span class="n">getParent</span><span class="p">();</span>
+
+  <span class="c1">// Register all variables and emit their initializer.</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">VarNames</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">VarName</span> <span class="o">=</span> <span class="n">VarNames</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">first</span><span class="p">;</span>
+    <span class="n">ExprAST</span> <span class="o">*</span><span class="n">Init</span> <span class="o">=</span> <span class="n">VarNames</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">second</span><span class="p">;</span>
+
+    <span class="c1">// Emit the initializer before adding the variable to scope, this prevents</span>
+    <span class="c1">// the initializer from referencing the variable itself, and permits stuff</span>
+    <span class="c1">// like this:</span>
+    <span class="c1">//  var a = 1 in</span>
+    <span class="c1">//    var a = a in ...   # refers to outer 'a'.</span>
+    <span class="n">Value</span> <span class="o">*</span><span class="n">InitVal</span><span class="p">;</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">Init</span><span class="p">)</span> <span class="p">{</span>
+      <span class="n">InitVal</span> <span class="o">=</span> <span class="n">Init</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+      <span class="k">if</span> <span class="p">(</span><span class="n">InitVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+        <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span> <span class="k">else</span> <span class="p">{</span> <span class="c1">// If not specified, use 0.0.</span>
+      <span class="n">InitVal</span> <span class="o">=</span> <span class="n">ConstantFP</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="n">APFloat</span><span class="p">(</span><span class="mf">0.0</span><span class="p">));</span>
+    <span class="p">}</span>
+
+    <span class="n">AllocaInst</span> <span class="o">*</span><span class="n">Alloca</span> <span class="o">=</span> <span class="n">CreateEntryBlockAlloca</span><span class="p">(</span><span class="n">TheFunction</span><span class="p">,</span> <span class="n">VarName</span><span class="p">);</span>
+    <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">InitVal</span><span class="p">,</span> <span class="n">Alloca</span><span class="p">);</span>
+
+    <span class="c1">// Remember the old variable binding so that we can restore the binding when</span>
+    <span class="c1">// we unrecurse.</span>
+    <span class="n">OldBindings</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]);</span>
+
+    <span class="c1">// Remember this binding.</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarName</span><span class="p">]</span> <span class="o">=</span> <span class="n">Alloca</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="k">this</span><span class="p">);</span>
+
+  <span class="c1">// Codegen the body, now that all vars are in scope.</span>
+  <span class="n">Value</span> <span class="o">*</span><span class="n">BodyVal</span> <span class="o">=</span> <span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">BodyVal</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Pop all our variables from scope.</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">VarNames</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">VarNames</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">first</span><span class="p">]</span> <span class="o">=</span> <span class="n">OldBindings</span><span class="p">[</span><span class="n">i</span><span class="p">];</span>
+
+  <span class="c1">// Return the body computation.</span>
+  <span class="k">return</span> <span class="n">BodyVal</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="n">Function</span> <span class="o">*</span><span class="n">PrototypeAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Make the function type:  double(double,double) etc.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">Type</span> <span class="o">*></span> <span class="n">Doubles</span><span class="p">(</span><span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">(),</span>
+                              <span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()));</span>
+  <span class="n">FunctionType</span> <span class="o">*</span><span class="n">FT</span> <span class="o">=</span>
+      <span class="n">FunctionType</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">Type</span><span class="o">::</span><span class="n">getDoubleTy</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">()),</span> <span class="n">Doubles</span><span class="p">,</span> <span class="nb">false</span><span class="p">);</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span>
+      <span class="n">Function</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">FT</span><span class="p">,</span> <span class="n">Function</span><span class="o">::</span><span class="n">ExternalLinkage</span><span class="p">,</span> <span class="n">Name</span><span class="p">,</span> <span class="n">TheModule</span><span class="p">);</span>
+
+  <span class="c1">// If F conflicted, there was already something named 'Name'.  If it has a</span>
+  <span class="c1">// body, don't allow redefinition or reextern.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">F</span><span class="o">-></span><span class="n">getName</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Name</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Delete the one we just made and get the existing one.</span>
+    <span class="n">F</span><span class="o">-></span><span class="n">eraseFromParent</span><span class="p">();</span>
+    <span class="n">F</span> <span class="o">=</span> <span class="n">TheModule</span><span class="o">-></span><span class="n">getFunction</span><span class="p">(</span><span class="n">Name</span><span class="p">);</span>
+
+    <span class="c1">// If F already has a body, reject this.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">F</span><span class="o">-></span><span class="n">empty</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">ErrorF</span><span class="p">(</span><span class="s">"redefinition of function"</span><span class="p">);</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+
+    <span class="c1">// If F took a different number of args, reject.</span>
+    <span class="k">if</span> <span class="p">(</span><span class="n">F</span><span class="o">-></span><span class="n">arg_size</span><span class="p">()</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">ErrorF</span><span class="p">(</span><span class="s">"redefinition of function with different # args"</span><span class="p">);</span>
+      <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Set names for all arguments.</span>
+  <span class="kt">unsigned</span> <span class="n">Idx</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+  <span class="k">for</span> <span class="p">(</span><span class="n">Function</span><span class="o">::</span><span class="n">arg_iterator</span> <span class="n">AI</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">arg_begin</span><span class="p">();</span> <span class="n">Idx</span> <span class="o">!=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span>
+       <span class="o">++</span><span class="n">AI</span><span class="p">,</span> <span class="o">++</span><span class="n">Idx</span><span class="p">)</span>
+    <span class="n">AI</span><span class="o">-></span><span class="n">setName</span><span class="p">(</span><span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]);</span>
+
+  <span class="c1">// Create a subprogram DIE for this function.</span>
+  <span class="n">DIFile</span> <span class="o">*</span><span class="n">Unit</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createFile</span><span class="p">(</span><span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">TheCU</span><span class="o">-></span><span class="n">getFilename</span><span class="p">(),</span>
+                                      <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">TheCU</span><span class="o">-></span><span class="n">getDirectory</span><span class="p">());</span>
+  <span class="n">DIScope</span> <span class="o">*</span><span class="n">FContext</span> <span class="o">=</span> <span class="n">Unit</span><span class="p">;</span>
+  <span class="kt">unsigned</span> <span class="n">LineNo</span> <span class="o">=</span> <span class="n">Line</span><span class="p">;</span>
+  <span class="kt">unsigned</span> <span class="n">ScopeLine</span> <span class="o">=</span> <span class="n">Line</span><span class="p">;</span>
+  <span class="n">DISubprogram</span> <span class="o">*</span><span class="n">SP</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createFunction</span><span class="p">(</span>
+      <span class="n">FContext</span><span class="p">,</span> <span class="n">Name</span><span class="p">,</span> <span class="n">StringRef</span><span class="p">(),</span> <span class="n">Unit</span><span class="p">,</span> <span class="n">LineNo</span><span class="p">,</span>
+      <span class="n">CreateFunctionType</span><span class="p">(</span><span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">(),</span> <span class="n">Unit</span><span class="p">),</span> <span class="nb">false</span> <span class="cm">/* internal linkage */</span><span class="p">,</span>
+      <span class="nb">true</span> <span class="cm">/* definition */</span><span class="p">,</span> <span class="n">ScopeLine</span><span class="p">,</span> <span class="n">DINode</span><span class="o">::</span><span class="n">FlagPrototyped</span><span class="p">,</span> <span class="nb">false</span><span class="p">,</span> <span class="n">F</span><span class="p">);</span>
+
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">FnScopeMap</span><span class="p">[</span><span class="k">this</span><span class="p">]</span> <span class="o">=</span> <span class="n">SP</span><span class="p">;</span>
+  <span class="k">return</span> <span class="n">F</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// CreateArgumentAllocas - Create an alloca for each argument and register the</span>
+<span class="c1">/// argument in the symbol table so that references to it will succeed.</span>
+<span class="kt">void</span> <span class="n">PrototypeAST</span><span class="o">::</span><span class="n">CreateArgumentAllocas</span><span class="p">(</span><span class="n">Function</span> <span class="o">*</span><span class="n">F</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">Function</span><span class="o">::</span><span class="n">arg_iterator</span> <span class="n">AI</span> <span class="o">=</span> <span class="n">F</span><span class="o">-></span><span class="n">arg_begin</span><span class="p">();</span>
+  <span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">Idx</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">e</span> <span class="o">=</span> <span class="n">Args</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="n">Idx</span> <span class="o">!=</span> <span class="n">e</span><span class="p">;</span> <span class="o">++</span><span class="n">Idx</span><span class="p">,</span> <span class="o">++</span><span class="n">AI</span><span class="p">)</span> <span class="p">{</span>
+    <span class="c1">// Create an alloca for this variable.</span>
+    <span class="n">AllocaInst</span> <span class="o">*</span><span class="n">Alloca</span> <span class="o">=</span> <span class="n">CreateEntryBlockAlloca</span><span class="p">(</span><span class="n">F</span><span class="p">,</span> <span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]);</span>
+
+    <span class="c1">// Create a debug descriptor for the variable.</span>
+    <span class="n">DIScope</span> <span class="o">*</span><span class="n">Scope</span> <span class="o">=</span> <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">LexicalBlocks</span><span class="p">.</span><span class="n">back</span><span class="p">();</span>
+    <span class="n">DIFile</span> <span class="o">*</span><span class="n">Unit</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createFile</span><span class="p">(</span><span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">TheCU</span><span class="o">-></span><span class="n">getFilename</span><span class="p">(),</span>
+                                        <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">TheCU</span><span class="o">-></span><span class="n">getDirectory</span><span class="p">());</span>
+    <span class="n">DILocalVariable</span> <span class="o">*</span><span class="n">D</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createLocalVariable</span><span class="p">(</span>
+        <span class="n">dwarf</span><span class="o">::</span><span class="n">DW_TAG_arg_variable</span><span class="p">,</span> <span class="n">Scope</span><span class="p">,</span> <span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">],</span> <span class="n">Unit</span><span class="p">,</span> <span class="n">Line</span><span class="p">,</span>
+        <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">getDoubleTy</span><span class="p">(),</span> <span class="n">Idx</span><span class="p">);</span>
+
+    <span class="n">DBuilder</span><span class="o">-></span><span class="n">insertDeclare</span><span class="p">(</span><span class="n">Alloca</span><span class="p">,</span> <span class="n">D</span><span class="p">,</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createExpression</span><span class="p">(),</span>
+                            <span class="n">DebugLoc</span><span class="o">::</span><span class="n">get</span><span class="p">(</span><span class="n">Line</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">Scope</span><span class="p">),</span>
+                            <span class="n">Builder</span><span class="p">.</span><span class="n">GetInsertBlock</span><span class="p">());</span>
+
+    <span class="c1">// Store the initial value into the alloca.</span>
+    <span class="n">Builder</span><span class="p">.</span><span class="n">CreateStore</span><span class="p">(</span><span class="n">AI</span><span class="p">,</span> <span class="n">Alloca</span><span class="p">);</span>
+
+    <span class="c1">// Add arguments to variable symbol table.</span>
+    <span class="n">NamedValues</span><span class="p">[</span><span class="n">Args</span><span class="p">[</span><span class="n">Idx</span><span class="p">]]</span> <span class="o">=</span> <span class="n">Alloca</span><span class="p">;</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="n">Function</span> <span class="o">*</span><span class="n">FunctionAST</span><span class="o">::</span><span class="n">Codegen</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">NamedValues</span><span class="p">.</span><span class="n">clear</span><span class="p">();</span>
+
+  <span class="n">Function</span> <span class="o">*</span><span class="n">TheFunction</span> <span class="o">=</span> <span class="n">Proto</span><span class="o">-></span><span class="n">Codegen</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">TheFunction</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
+    <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Push the current scope.</span>
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">LexicalBlocks</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">FnScopeMap</span><span class="p">[</span><span class="n">Proto</span><span class="p">]);</span>
+
+  <span class="c1">// Unset the location for the prologue emission (leading instructions with no</span>
+  <span class="c1">// location in a function are considered part of the prologue and the debugger</span>
+  <span class="c1">// will run past them when breaking on a function)</span>
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="n">nullptr</span><span class="p">);</span>
+
+  <span class="c1">// If this is an operator, install it.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Proto</span><span class="o">-></span><span class="n">isBinaryOp</span><span class="p">())</span>
+    <span class="n">BinopPrecedence</span><span class="p">[</span><span class="n">Proto</span><span class="o">-></span><span class="n">getOperatorName</span><span class="p">()]</span> <span class="o">=</span> <span class="n">Proto</span><span class="o">-></span><span class="n">getBinaryPrecedence</span><span class="p">();</span>
+
+  <span class="c1">// Create a new basic block to start insertion into.</span>
+  <span class="n">BasicBlock</span> <span class="o">*</span><span class="n">BB</span> <span class="o">=</span> <span class="n">BasicBlock</span><span class="o">::</span><span class="n">Create</span><span class="p">(</span><span class="n">getGlobalContext</span><span class="p">(),</span> <span class="s">"entry"</span><span class="p">,</span> <span class="n">TheFunction</span><span class="p">);</span>
+  <span class="n">Builder</span><span class="p">.</span><span class="n">SetInsertPoint</span><span class="p">(</span><span class="n">BB</span><span class="p">);</span>
+
+  <span class="c1">// Add all arguments to the symbol table and create their allocas.</span>
+  <span class="n">Proto</span><span class="o">-></span><span class="n">CreateArgumentAllocas</span><span class="p">(</span><span class="n">TheFunction</span><span class="p">);</span>
+
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">emitLocation</span><span class="p">(</span><span class="n">Body</span><span class="p">);</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">Value</span> <span class="o">*</span><span class="n">RetVal</span> <span class="o">=</span> <span class="n">Body</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+    <span class="c1">// Finish off the function.</span>
+    <span class="n">Builder</span><span class="p">.</span><span class="n">CreateRet</span><span class="p">(</span><span class="n">RetVal</span><span class="p">);</span>
+
+    <span class="c1">// Pop off the lexical block for the function.</span>
+    <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">LexicalBlocks</span><span class="p">.</span><span class="n">pop_back</span><span class="p">();</span>
+
+    <span class="c1">// Validate the generated code, checking for consistency.</span>
+    <span class="n">verifyFunction</span><span class="p">(</span><span class="o">*</span><span class="n">TheFunction</span><span class="p">);</span>
+
+    <span class="c1">// Optimize the function.</span>
+    <span class="n">TheFPM</span><span class="o">-></span><span class="n">run</span><span class="p">(</span><span class="o">*</span><span class="n">TheFunction</span><span class="p">);</span>
+
+    <span class="k">return</span> <span class="n">TheFunction</span><span class="p">;</span>
+  <span class="p">}</span>
+
+  <span class="c1">// Error reading body, remove function.</span>
+  <span class="n">TheFunction</span><span class="o">-></span><span class="n">eraseFromParent</span><span class="p">();</span>
+
+  <span class="k">if</span> <span class="p">(</span><span class="n">Proto</span><span class="o">-></span><span class="n">isBinaryOp</span><span class="p">())</span>
+    <span class="n">BinopPrecedence</span><span class="p">.</span><span class="n">erase</span><span class="p">(</span><span class="n">Proto</span><span class="o">-></span><span class="n">getOperatorName</span><span class="p">());</span>
+
+  <span class="c1">// Pop off the lexical block for the function since we added it</span>
+  <span class="c1">// unconditionally.</span>
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">LexicalBlocks</span><span class="p">.</span><span class="n">pop_back</span><span class="p">();</span>
+
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Top-Level parsing and JIT Driver</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="k">static</span> <span class="n">ExecutionEngine</span> <span class="o">*</span><span class="n">TheExecutionEngine</span><span class="p">;</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleDefinition</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">FunctionAST</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">ParseDefinition</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">F</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Error reading function definition:"</span><span class="p">);</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleExtern</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">PrototypeAST</span> <span class="o">*</span><span class="n">P</span> <span class="o">=</span> <span class="n">ParseExtern</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">P</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Error reading extern"</span><span class="p">);</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">HandleTopLevelExpression</span><span class="p">()</span> <span class="p">{</span>
+  <span class="c1">// Evaluate a top-level expression into an anonymous function.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">FunctionAST</span> <span class="o">*</span><span class="n">F</span> <span class="o">=</span> <span class="n">ParseTopLevelExpr</span><span class="p">())</span> <span class="p">{</span>
+    <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">F</span><span class="o">-></span><span class="n">Codegen</span><span class="p">())</span> <span class="p">{</span>
+      <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Error generating code for top level expr"</span><span class="p">);</span>
+    <span class="p">}</span>
+  <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
+    <span class="c1">// Skip token for error recovery.</span>
+    <span class="n">getNextToken</span><span class="p">();</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">/// top ::= definition | external | expression | ';'</span>
+<span class="k">static</span> <span class="kt">void</span> <span class="nf">MainLoop</span><span class="p">()</span> <span class="p">{</span>
+  <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">switch</span> <span class="p">(</span><span class="n">CurTok</span><span class="p">)</span> <span class="p">{</span>
+    <span class="k">case</span> <span class="n">tok_eof</span>:
+      <span class="k">return</span><span class="p">;</span>
+    <span class="k">case</span> <span class="sc">';'</span>:
+      <span class="n">getNextToken</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span> <span class="c1">// ignore top-level semicolons.</span>
+    <span class="k">case</span> <span class="n">tok_def</span>:
+      <span class="n">HandleDefinition</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="k">case</span> <span class="n">tok_extern</span>:
+      <span class="n">HandleExtern</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="nl">default:</span>
+      <span class="n">HandleTopLevelExpression</span><span class="p">();</span>
+      <span class="k">break</span><span class="p">;</span>
+    <span class="p">}</span>
+  <span class="p">}</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// "Library" functions that can be "extern'd" from user code.</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="c1">/// putchard - putchar that takes a double and returns 0.</span>
+<span class="k">extern</span> <span class="s">"C"</span> <span class="kt">double</span> <span class="n">putchard</span><span class="p">(</span><span class="kt">double</span> <span class="n">X</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">putchar</span><span class="p">((</span><span class="kt">char</span><span class="p">)</span><span class="n">X</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">/// printd - printf that takes a double prints it as "%f\n", returning 0.</span>
+<span class="k">extern</span> <span class="s">"C"</span> <span class="kt">double</span> <span class="n">printd</span><span class="p">(</span><span class="kt">double</span> <span class="n">X</span><span class="p">)</span> <span class="p">{</span>
+  <span class="n">printf</span><span class="p">(</span><span class="s">"%f</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">X</span><span class="p">);</span>
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+<span class="c1">// Main driver code.</span>
+<span class="c1">//===----------------------------------------------------------------------===//</span>
+
+<span class="kt">int</span> <span class="n">main</span><span class="p">()</span> <span class="p">{</span>
+  <span class="n">InitializeNativeTarget</span><span class="p">();</span>
+  <span class="n">InitializeNativeTargetAsmPrinter</span><span class="p">();</span>
+  <span class="n">InitializeNativeTargetAsmParser</span><span class="p">();</span>
+  <span class="n">LLVMContext</span> <span class="o">&</span><span class="n">Context</span> <span class="o">=</span> <span class="n">getGlobalContext</span><span class="p">();</span>
+
+  <span class="c1">// Install standard binary operators.</span>
+  <span class="c1">// 1 is lowest precedence.</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'='</span><span class="p">]</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'<'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">10</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'+'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'-'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span>
+  <span class="n">BinopPrecedence</span><span class="p">[</span><span class="sc">'*'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">40</span><span class="p">;</span> <span class="c1">// highest.</span>
+
+  <span class="c1">// Prime the first token.</span>
+  <span class="n">getNextToken</span><span class="p">();</span>
+
+  <span class="c1">// Make the module, which holds all the code.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">unique_ptr</span><span class="o"><</span><span class="n">Module</span><span class="o">></span> <span class="n">Owner</span> <span class="o">=</span> <span class="n">make_unique</span><span class="o"><</span><span class="n">Module</span><span class="o">></span><span class="p">(</span><span class="s">"my cool jit"</span><span class="p">,</span> <span class="n">Context</span><span class="p">);</span>
+  <span class="n">TheModule</span> <span class="o">=</span> <span class="n">Owner</span><span class="p">.</span><span class="n">get</span><span class="p">();</span>
+
+  <span class="c1">// Add the current debug info version into the module.</span>
+  <span class="n">TheModule</span><span class="o">-></span><span class="n">addModuleFlag</span><span class="p">(</span><span class="n">Module</span><span class="o">::</span><span class="n">Warning</span><span class="p">,</span> <span class="s">"Debug Info Version"</span><span class="p">,</span>
+                           <span class="n">DEBUG_METADATA_VERSION</span><span class="p">);</span>
+
+  <span class="c1">// Darwin only supports dwarf2.</span>
+  <span class="k">if</span> <span class="p">(</span><span class="n">Triple</span><span class="p">(</span><span class="n">sys</span><span class="o">::</span><span class="n">getProcessTriple</span><span class="p">()).</span><span class="n">isOSDarwin</span><span class="p">())</span>
+    <span class="n">TheModule</span><span class="o">-></span><span class="n">addModuleFlag</span><span class="p">(</span><span class="n">llvm</span><span class="o">::</span><span class="n">Module</span><span class="o">::</span><span class="n">Warning</span><span class="p">,</span> <span class="s">"Dwarf Version"</span><span class="p">,</span> <span class="mi">2</span><span class="p">);</span>
+
+  <span class="c1">// Construct the DIBuilder, we do this here because we need the module.</span>
+  <span class="n">DBuilder</span> <span class="o">=</span> <span class="k">new</span> <span class="n">DIBuilder</span><span class="p">(</span><span class="o">*</span><span class="n">TheModule</span><span class="p">);</span>
+
+  <span class="c1">// Create the compile unit for the module.</span>
+  <span class="c1">// Currently down as "fib.ks" as a filename since we're redirecting stdin</span>
+  <span class="c1">// but we'd like actual source locations.</span>
+  <span class="n">KSDbgInfo</span><span class="p">.</span><span class="n">TheCU</span> <span class="o">=</span> <span class="n">DBuilder</span><span class="o">-></span><span class="n">createCompileUnit</span><span class="p">(</span>
+      <span class="n">dwarf</span><span class="o">::</span><span class="n">DW_LANG_C</span><span class="p">,</span> <span class="s">"fib.ks"</span><span class="p">,</span> <span class="s">"."</span><span class="p">,</span> <span class="s">"Kaleidoscope Compiler"</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="s">""</span><span class="p">,</span> <span class="mi">0</span><span class="p">);</span>
+
+  <span class="c1">// Create the JIT.  This takes ownership of the module.</span>
+  <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">ErrStr</span><span class="p">;</span>
+  <span class="n">TheExecutionEngine</span> <span class="o">=</span>
+      <span class="n">EngineBuilder</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">move</span><span class="p">(</span><span class="n">Owner</span><span class="p">))</span>
+          <span class="p">.</span><span class="n">setErrorStr</span><span class="p">(</span><span class="o">&</span><span class="n">ErrStr</span><span class="p">)</span>
+          <span class="p">.</span><span class="n">setMCJITMemoryManager</span><span class="p">(</span><span class="n">llvm</span><span class="o">::</span><span class="n">make_unique</span><span class="o"><</span><span class="n">SectionMemoryManager</span><span class="o">></span><span class="p">())</span>
+          <span class="p">.</span><span class="n">create</span><span class="p">();</span>
+  <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">TheExecutionEngine</span><span class="p">)</span> <span class="p">{</span>
+    <span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Could not create ExecutionEngine: %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">ErrStr</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span>
+    <span class="n">exit</span><span class="p">(</span><span class="mi">1</span><span class="p">);</span>
+  <span class="p">}</span>
+
+  <span class="n">legacy</span><span class="o">::</span><span class="n">FunctionPassManager</span> <span class="n">OurFPM</span><span class="p">(</span><span class="n">TheModule</span><span class="p">);</span>
+
+  <span class="c1">// Set up the optimizer pipeline.  Start with registering info about how the</span>
+  <span class="c1">// target lays out data structures.</span>
+  <span class="n">TheModule</span><span class="o">-></span><span class="n">setDataLayout</span><span class="p">(</span><span class="o">*</span><span class="n">TheExecutionEngine</span><span class="o">-></span><span class="n">getDataLayout</span><span class="p">());</span>
+<span class="cp">#if 0</span><span class="c"></span>
+<span class="c">  // Provide basic AliasAnalysis support for GVN.</span>
+<span class="c">  OurFPM.add(createBasicAliasAnalysisPass());</span>
+<span class="c">  // Promote allocas to registers.</span>
+<span class="c">  OurFPM.add(createPromoteMemoryToRegisterPass());</span>
+<span class="c">  // Do simple "peephole" optimizations and bit-twiddling optzns.</span>
+<span class="c">  OurFPM.add(createInstructionCombiningPass());</span>
+<span class="c">  // Reassociate expressions.</span>
+<span class="c">  OurFPM.add(createReassociatePass());</span>
+<span class="c">  // Eliminate Common SubExpressions.</span>
+<span class="c">  OurFPM.add(createGVNPass());</span>
+<span class="c">  // Simplify the control flow graph (deleting unreachable blocks, etc).</span>
+<span class="c">  OurFPM.add(createCFGSimplificationPass());</span>
+<span class="cp">  #endif</span>
+  <span class="n">OurFPM</span><span class="p">.</span><span class="n">doInitialization</span><span class="p">();</span>
+
+  <span class="c1">// Set the global so the code gen can use this.</span>
+  <span class="n">TheFPM</span> <span class="o">=</span> <span class="o">&</span><span class="n">OurFPM</span><span class="p">;</span>
+
+  <span class="c1">// Run the main "interpreter loop" now.</span>
+  <span class="n">MainLoop</span><span class="p">();</span>
+
+  <span class="n">TheFPM</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
+
+  <span class="c1">// Finalize the debug info.</span>
+  <span class="n">DBuilder</span><span class="o">-></span><span class="n">finalize</span><span class="p">();</span>
+
+  <span class="c1">// Print out all of the generated code.</span>
+  <span class="n">TheModule</span><span class="o">-></span><span class="n">dump</span><span class="p">();</span>
+
+  <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
+<span class="p">}</span>
+</pre></div>
+</div>
+<p><a class="reference external" href="LangImpl9.html">Next: Conclusion and other useful LLVM tidbits</a></p>
+</div>
+</div>
+
+
+          </div>
+      </div>
+      <div class="clearer"></div>
+    </div>
+    <div class="related">
+      <h3>Navigation</h3>
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+             >previous</a> |</li>
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+  <div class="section" id="kaleidoscope-conclusion-and-other-useful-llvm-tidbits">
+<h1>9. Kaleidoscope: Conclusion and other useful LLVM tidbits<a class="headerlink" href="#kaleidoscope-conclusion-and-other-useful-llvm-tidbits" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#tutorial-conclusion" id="id2">Tutorial Conclusion</a></li>
+<li><a class="reference internal" href="#properties-of-the-llvm-ir" id="id3">Properties of the LLVM IR</a><ul>
+<li><a class="reference internal" href="#target-independence" id="id4">Target Independence</a></li>
+<li><a class="reference internal" href="#safety-guarantees" id="id5">Safety Guarantees</a></li>
+<li><a class="reference internal" href="#language-specific-optimizations" id="id6">Language-Specific Optimizations</a></li>
+</ul>
+</li>
+<li><a class="reference internal" href="#tips-and-tricks" id="id7">Tips and Tricks</a><ul>
+<li><a class="reference internal" href="#implementing-portable-offsetof-sizeof" id="id8">Implementing portable offsetof/sizeof</a></li>
+<li><a class="reference internal" href="#garbage-collected-stack-frames" id="id9">Garbage Collected Stack Frames</a></li>
+</ul>
+</li>
+</ul>
+</div>
+<div class="section" id="tutorial-conclusion">
+<h2><a class="toc-backref" href="#id2">9.1. Tutorial Conclusion</a><a class="headerlink" href="#tutorial-conclusion" title="Permalink to this headline">¶</a></h2>
+<p>Welcome to the final chapter of the “<a class="reference external" href="index.html">Implementing a language with
+LLVM</a>” tutorial. In the course of this tutorial, we have
+grown our little Kaleidoscope language from being a useless toy, to
+being a semi-interesting (but probably still useless) toy. :)</p>
+<p>It is interesting to see how far we’ve come, and how little code it has
+taken. We built the entire lexer, parser, AST, code generator, an
+interactive run-loop (with a JIT!), and emitted debug information in
+standalone executables - all in under 1000 lines of (non-comment/non-blank)
+code.</p>
+<p>Our little language supports a couple of interesting features: it
+supports user defined binary and unary operators, it uses JIT
+compilation for immediate evaluation, and it supports a few control flow
+constructs with SSA construction.</p>
+<p>Part of the idea of this tutorial was to show you how easy and fun it
+can be to define, build, and play with languages. Building a compiler
+need not be a scary or mystical process! Now that you’ve seen some of
+the basics, I strongly encourage you to take the code and hack on it.
+For example, try adding:</p>
+<ul class="simple">
+<li><strong>global variables</strong> - While global variables have questional value
+in modern software engineering, they are often useful when putting
+together quick little hacks like the Kaleidoscope compiler itself.
+Fortunately, our current setup makes it very easy to add global
+variables: just have value lookup check to see if an unresolved
+variable is in the global variable symbol table before rejecting it.
+To create a new global variable, make an instance of the LLVM
+<tt class="docutils literal"><span class="pre">GlobalVariable</span></tt> class.</li>
+<li><strong>typed variables</strong> - Kaleidoscope currently only supports variables
+of type double. This gives the language a very nice elegance, because
+only supporting one type means that you never have to specify types.
+Different languages have different ways of handling this. The easiest
+way is to require the user to specify types for every variable
+definition, and record the type of the variable in the symbol table
+along with its Value*.</li>
+<li><strong>arrays, structs, vectors, etc</strong> - Once you add types, you can start
+extending the type system in all sorts of interesting ways. Simple
+arrays are very easy and are quite useful for many different
+applications. Adding them is mostly an exercise in learning how the
+LLVM <a class="reference external" href="../LangRef.html#i_getelementptr">getelementptr</a> instruction
+works: it is so nifty/unconventional, it <a class="reference external" href="../GetElementPtr.html">has its own
+FAQ</a>! If you add support for recursive types
+(e.g. linked lists), make sure to read the <a class="reference external" href="../ProgrammersManual.html#TypeResolve">section in the LLVM
+Programmer’s Manual</a> that
+describes how to construct them.</li>
+<li><strong>standard runtime</strong> - Our current language allows the user to access
+arbitrary external functions, and we use it for things like “printd”
+and “putchard”. As you extend the language to add higher-level
+constructs, often these constructs make the most sense if they are
+lowered to calls into a language-supplied runtime. For example, if
+you add hash tables to the language, it would probably make sense to
+add the routines to a runtime, instead of inlining them all the way.</li>
+<li><strong>memory management</strong> - Currently we can only access the stack in
+Kaleidoscope. It would also be useful to be able to allocate heap
+memory, either with calls to the standard libc malloc/free interface
+or with a garbage collector. If you would like to use garbage
+collection, note that LLVM fully supports <a class="reference external" href="../GarbageCollection.html">Accurate Garbage
+Collection</a> including algorithms that
+move objects and need to scan/update the stack.</li>
+<li><strong>exception handling support</strong> - LLVM supports generation of <a class="reference external" href="../ExceptionHandling.html">zero
+cost exceptions</a> which interoperate with
+code compiled in other languages. You could also generate code by
+implicitly making every function return an error value and checking
+it. You could also make explicit use of setjmp/longjmp. There are
+many different ways to go here.</li>
+<li><strong>object orientation, generics, database access, complex numbers,
+geometric programming, ...</strong> - Really, there is no end of crazy
+features that you can add to the language.</li>
+<li><strong>unusual domains</strong> - We’ve been talking about applying LLVM to a
+domain that many people are interested in: building a compiler for a
+specific language. However, there are many other domains that can use
+compiler technology that are not typically considered. For example,
+LLVM has been used to implement OpenGL graphics acceleration,
+translate C++ code to ActionScript, and many other cute and clever
+things. Maybe you will be the first to JIT compile a regular
+expression interpreter into native code with LLVM?</li>
+</ul>
+<p>Have fun - try doing something crazy and unusual. Building a language
+like everyone else always has, is much less fun than trying something a
+little crazy or off the wall and seeing how it turns out. If you get
+stuck or want to talk about it, feel free to email the <a class="reference external" href="http://lists.llvm.org/mailman/listinfo/llvm-dev">llvm-dev mailing
+list</a>: it has lots
+of people who are interested in languages and are often willing to help
+out.</p>
+<p>Before we end this tutorial, I want to talk about some “tips and tricks”
+for generating LLVM IR. These are some of the more subtle things that
+may not be obvious, but are very useful if you want to take advantage of
+LLVM’s capabilities.</p>
+</div>
+<div class="section" id="properties-of-the-llvm-ir">
+<h2><a class="toc-backref" href="#id3">9.2. Properties of the LLVM IR</a><a class="headerlink" href="#properties-of-the-llvm-ir" title="Permalink to this headline">¶</a></h2>
+<p>We have a couple common questions about code in the LLVM IR form - lets
+just get these out of the way right now, shall we?</p>
+<div class="section" id="target-independence">
+<h3><a class="toc-backref" href="#id4">9.2.1. Target Independence</a><a class="headerlink" href="#target-independence" title="Permalink to this headline">¶</a></h3>
+<p>Kaleidoscope is an example of a “portable language”: any program written
+in Kaleidoscope will work the same way on any target that it runs on.
+Many other languages have this property, e.g. lisp, java, haskell,
+javascript, python, etc (note that while these languages are portable,
+not all their libraries are).</p>
+<p>One nice aspect of LLVM is that it is often capable of preserving target
+independence in the IR: you can take the LLVM IR for a
+Kaleidoscope-compiled program and run it on any target that LLVM
+supports, even emitting C code and compiling that on targets that LLVM
+doesn’t support natively. You can trivially tell that the Kaleidoscope
+compiler generates target-independent code because it never queries for
+any target-specific information when generating code.</p>
+<p>The fact that LLVM provides a compact, target-independent,
+representation for code gets a lot of people excited. Unfortunately,
+these people are usually thinking about C or a language from the C
+family when they are asking questions about language portability. I say
+“unfortunately”, because there is really no way to make (fully general)
+C code portable, other than shipping the source code around (and of
+course, C source code is not actually portable in general either - ever
+port a really old application from 32- to 64-bits?).</p>
+<p>The problem with C (again, in its full generality) is that it is heavily
+laden with target specific assumptions. As one simple example, the
+preprocessor often destructively removes target-independence from the
+code when it processes the input text:</p>
+<div class="highlight-c"><div class="highlight"><pre><span class="cp">#ifdef __i386__</span>
+  <span class="kt">int</span> <span class="n">X</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span>
+<span class="cp">#else</span>
+  <span class="kt">int</span> <span class="n">X</span> <span class="o">=</span> <span class="mi">42</span><span class="p">;</span>
+<span class="cp">#endif</span>
+</pre></div>
+</div>
+<p>While it is possible to engineer more and more complex solutions to
+problems like this, it cannot be solved in full generality in a way that
+is better than shipping the actual source code.</p>
+<p>That said, there are interesting subsets of C that can be made portable.
+If you are willing to fix primitive types to a fixed size (say int =
+32-bits, and long = 64-bits), don’t care about ABI compatibility with
+existing binaries, and are willing to give up some other minor features,
+you can have portable code. This can make sense for specialized domains
+such as an in-kernel language.</p>
+</div>
+<div class="section" id="safety-guarantees">
+<h3><a class="toc-backref" href="#id5">9.2.2. Safety Guarantees</a><a class="headerlink" href="#safety-guarantees" title="Permalink to this headline">¶</a></h3>
+<p>Many of the languages above are also “safe” languages: it is impossible
+for a program written in Java to corrupt its address space and crash the
+process (assuming the JVM has no bugs). Safety is an interesting
+property that requires a combination of language design, runtime
+support, and often operating system support.</p>
+<p>It is certainly possible to implement a safe language in LLVM, but LLVM
+IR does not itself guarantee safety. The LLVM IR allows unsafe pointer
+casts, use after free bugs, buffer over-runs, and a variety of other
+problems. Safety needs to be implemented as a layer on top of LLVM and,
+conveniently, several groups have investigated this. Ask on the <a class="reference external" href="http://lists.llvm.org/mailman/listinfo/llvm-dev">llvm-dev
+mailing list</a> if
+you are interested in more details.</p>
+</div>
+<div class="section" id="language-specific-optimizations">
+<h3><a class="toc-backref" href="#id6">9.2.3. Language-Specific Optimizations</a><a class="headerlink" href="#language-specific-optimizations" title="Permalink to this headline">¶</a></h3>
+<p>One thing about LLVM that turns off many people is that it does not
+solve all the world’s problems in one system (sorry ‘world hunger’,
+someone else will have to solve you some other day). One specific
+complaint is that people perceive LLVM as being incapable of performing
+high-level language-specific optimization: LLVM “loses too much
+information”.</p>
+<p>Unfortunately, this is really not the place to give you a full and
+unified version of “Chris Lattner’s theory of compiler design”. Instead,
+I’ll make a few observations:</p>
+<p>First, you’re right that LLVM does lose information. For example, as of
+this writing, there is no way to distinguish in the LLVM IR whether an
+SSA-value came from a C “int” or a C “long” on an ILP32 machine (other
+than debug info). Both get compiled down to an ‘i32’ value and the
+information about what it came from is lost. The more general issue
+here, is that the LLVM type system uses “structural equivalence” instead
+of “name equivalence”. Another place this surprises people is if you
+have two types in a high-level language that have the same structure
+(e.g. two different structs that have a single int field): these types
+will compile down into a single LLVM type and it will be impossible to
+tell what it came from.</p>
+<p>Second, while LLVM does lose information, LLVM is not a fixed target: we
+continue to enhance and improve it in many different ways. In addition
+to adding new features (LLVM did not always support exceptions or debug
+info), we also extend the IR to capture important information for
+optimization (e.g. whether an argument is sign or zero extended,
+information about pointers aliasing, etc). Many of the enhancements are
+user-driven: people want LLVM to include some specific feature, so they
+go ahead and extend it.</p>
+<p>Third, it is <em>possible and easy</em> to add language-specific optimizations,
+and you have a number of choices in how to do it. As one trivial
+example, it is easy to add language-specific optimization passes that
+“know” things about code compiled for a language. In the case of the C
+family, there is an optimization pass that “knows” about the standard C
+library functions. If you call “exit(0)” in main(), it knows that it is
+safe to optimize that into “return 0;” because C specifies what the
+‘exit’ function does.</p>
+<p>In addition to simple library knowledge, it is possible to embed a
+variety of other language-specific information into the LLVM IR. If you
+have a specific need and run into a wall, please bring the topic up on
+the llvm-dev list. At the very worst, you can always treat LLVM as if it
+were a “dumb code generator” and implement the high-level optimizations
+you desire in your front-end, on the language-specific AST.</p>
+</div>
+</div>
+<div class="section" id="tips-and-tricks">
+<h2><a class="toc-backref" href="#id7">9.3. Tips and Tricks</a><a class="headerlink" href="#tips-and-tricks" title="Permalink to this headline">¶</a></h2>
+<p>There is a variety of useful tips and tricks that you come to know after
+working on/with LLVM that aren’t obvious at first glance. Instead of
+letting everyone rediscover them, this section talks about some of these
+issues.</p>
+<div class="section" id="implementing-portable-offsetof-sizeof">
+<h3><a class="toc-backref" href="#id8">9.3.1. Implementing portable offsetof/sizeof</a><a class="headerlink" href="#implementing-portable-offsetof-sizeof" title="Permalink to this headline">¶</a></h3>
+<p>One interesting thing that comes up, if you are trying to keep the code
+generated by your compiler “target independent”, is that you often need
+to know the size of some LLVM type or the offset of some field in an
+llvm structure. For example, you might need to pass the size of a type
+into a function that allocates memory.</p>
+<p>Unfortunately, this can vary widely across targets: for example the
+width of a pointer is trivially target-specific. However, there is a
+<a class="reference external" href="http://nondot.org/sabre/LLVMNotes/SizeOf-OffsetOf-VariableSizedStructs.txt">clever way to use the getelementptr
+instruction</a>
+that allows you to compute this in a portable way.</p>
+</div>
+<div class="section" id="garbage-collected-stack-frames">
+<h3><a class="toc-backref" href="#id9">9.3.2. Garbage Collected Stack Frames</a><a class="headerlink" href="#garbage-collected-stack-frames" title="Permalink to this headline">¶</a></h3>
+<p>Some languages want to explicitly manage their stack frames, often so
+that they are garbage collected or to allow easy implementation of
+closures. There are often better ways to implement these features than
+explicit stack frames, but <a class="reference external" href="http://nondot.org/sabre/LLVMNotes/ExplicitlyManagedStackFrames.txt">LLVM does support
+them,</a>
+if you want. It requires your front-end to convert the code into
+<a class="reference external" href="http://en.wikipedia.org/wiki/Continuation-passing_style">Continuation Passing
+Style</a> and
+the use of tail calls (which LLVM also supports).</p>
+</div>
+</div>
+</div>
+
+
+          </div>
+      </div>
+      <div class="clearer"></div>
+    </div>
+    <div class="related">
+      <h3>Navigation</h3>
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+            
+  <div class="section" id="kaleidoscope-tutorial-introduction-and-the-lexer">
+<h1>1. Kaleidoscope: Tutorial Introduction and the Lexer<a class="headerlink" href="#kaleidoscope-tutorial-introduction-and-the-lexer" title="Permalink to this headline">¶</a></h1>
+<div class="contents local topic" id="contents">
+<ul class="simple">
+<li><a class="reference internal" href="#tutorial-introduction" id="id1">Tutorial Introduction</a></li>
+<li><a class="reference internal" href="#the-basic-language" id="id2">The Basic Language</a></li>
+<li><a class="reference internal" href="#the-lexer" id="id3">The Lexer</a></li>
+</ul>
+</div>
+<div class="section" id="tutorial-introduction">
+<h2><a class="toc-backref" href="#id1">1.1. Tutorial Introduction</a><a class="headerlink" href="#tutorial-introduction" title="Permalink to this headline">¶</a></h2>
+<p>Welcome to the “Implementing a language with LLVM” tutorial. This
+tutorial runs through the implementation of a simple language, showing
+how fun and easy it can be. This tutorial will get you up and started as
+well as help to build a framework you can extend to other languages. The
+code in this tutorial can also be used as a playground to hack on other
+LLVM specific things.</p>
+<p>The goal of this tutorial is to progressively unveil our language,
+describing how it is built up over time. This will let us cover a fairly
+broad range of language design and LLVM-specific usage issues, showing
+and explaining the code for it all along the way, without overwhelming
+you with tons of details up front.</p>
+<p>It is useful to point out ahead of time that this tutorial is really
+about teaching compiler techniques and LLVM specifically, <em>not</em> about
+teaching modern and sane software engineering principles. In practice,
+this means that we’ll take a number of shortcuts to simplify the
+exposition. For example, the code leaks memory, uses global variables
+all over the place, doesn’t use nice design patterns like
+<a class="reference external" href="http://en.wikipedia.org/wiki/Visitor_pattern">visitors</a>, etc... but
+it is very simple. If you dig in and use the code as a basis for future
+projects, fixing these deficiencies shouldn’t be hard.</p>
+<p>I’ve tried to put this tutorial together in a way that makes chapters
+easy to skip over if you are already familiar with or are uninterested
+in the various pieces. The structure of the tutorial is:</p>
+<ul class="simple">
+<li><a class="reference external" href="#language">Chapter #1</a>: Introduction to the Kaleidoscope
+language, and the definition of its Lexer - This shows where we are
+going and the basic functionality that we want it to do. In order to
+make this tutorial maximally understandable and hackable, we choose
+to implement everything in Objective Caml instead of using lexer and
+parser generators. LLVM obviously works just fine with such tools,
+feel free to use one if you prefer.</li>
+<li><a class="reference external" href="OCamlLangImpl2.html">Chapter #2</a>: Implementing a Parser and
+AST - With the lexer in place, we can talk about parsing techniques
+and basic AST construction. This tutorial describes recursive descent
+parsing and operator precedence parsing. Nothing in Chapters 1 or 2
+is LLVM-specific, the code doesn’t even link in LLVM at this point.
+:)</li>
+<li><a class="reference external" href="OCamlLangImpl3.html">Chapter #3</a>: Code generation to LLVM IR -
+With the AST ready, we can show off how easy generation of LLVM IR
+really is.</li>
+<li><a class="reference external" href="OCamlLangImpl4.html">Chapter #4</a>: Adding JIT and Optimizer
+Support - Because a lot of people are interested in using LLVM as a
+JIT, we’ll dive right into it and show you the 3 lines it takes to
+add JIT support. LLVM is also useful in many other ways, but this is
+one simple and “sexy” way to shows off its power. :)</li>
+<li><a class="reference external" href="OCamlLangImpl5.html">Chapter #5</a>: Extending the Language:
+Control Flow - With the language up and running, we show how to
+extend it with control flow operations (if/then/else and a ‘for’
+loop). This gives us a chance to talk about simple SSA construction
+and control flow.</li>
+<li><a class="reference external" href="OCamlLangImpl6.html">Chapter #6</a>: Extending the Language:
+User-defined Operators - This is a silly but fun chapter that talks
+about extending the language to let the user program define their own
+arbitrary unary and binary operators (with assignable precedence!).
+This lets us build a significant piece of the “language” as library
+routines.</li>
+<li><a class="reference external" href="OCamlLangImpl7.html">Chapter #7</a>: Extending the Language:
+Mutable Variables - This chapter talks about adding user-defined
+local variables along with an assignment operator. The interesting
+part about this is how easy and trivial it is to construct SSA form
+in LLVM: no, LLVM does <em>not</em> require your front-end to construct SSA
+form!</li>
+<li><a class="reference external" href="OCamlLangImpl8.html">Chapter #8</a>: Conclusion and other useful
+LLVM tidbits - This chapter wraps up the series by talking about
+potential ways to extend the language, but also includes a bunch of
+pointers to info about “special topics” like adding garbage
+collection support, exceptions, debugging, support for “spaghetti
+stacks”, and a bunch of other tips and tricks.</li>
+</ul>
+<p>By the end of the tutorial, we’ll have written a bit less than 700 lines
+of non-comment, non-blank, lines of code. With this small amount of
+code, we’ll have built up a very reasonable compiler for a non-trivial
+language including a hand-written lexer, parser, AST, as well as code
+generation support with a JIT compiler. While other systems may have
+interesting “hello world” tutorials, I think the breadth of this
+tutorial is a great testament to the strengths of LLVM and why you
+should consider it if you’re interested in language or compiler design.</p>
+<p>A note about this tutorial: we expect you to extend the language and
+play with it on your own. Take the code and go crazy hacking away at it,
+compilers don’t need to be scary creatures - it can be a lot of fun to
+play with languages!</p>
+</div>
+<div class="section" id="the-basic-language">
+<h2><a class="toc-backref" href="#id2">1.2. The Basic Language</a><a class="headerlink" href="#the-basic-language" title="Permalink to this headline">¶</a></h2>
+<p>This tutorial will be illustrated with a toy language that we’ll call
+“<a class="reference external" href="http://en.wikipedia.org/wiki/Kaleidoscope">Kaleidoscope</a>” (derived
+from “meaning beautiful, form, and view”). Kaleidoscope is a procedural
+language that allows you to define functions, use conditionals, math,
+etc. Over the course of the tutorial, we’ll extend Kaleidoscope to
+support the if/then/else construct, a for loop, user defined operators,
+JIT compilation with a simple command line interface, etc.</p>
+<p>Because we want to keep things simple, the only datatype in Kaleidoscope
+is a 64-bit floating point type (aka ‘float’ in O’Caml parlance). As
+such, all values are implicitly double precision and the language
+doesn’t require type declarations. This gives the language a very nice
+and simple syntax. For example, the following simple example computes
+<a class="reference external" href="http://en.wikipedia.org/wiki/Fibonacci_number">Fibonacci numbers:</a></p>
+<div class="highlight-python"><div class="highlight"><pre># Compute the x'th fibonacci number.
+def fib(x)
+  if x < 3 then
+    1
+  else
+    fib(x-1)+fib(x-2)
+
+# This expression will compute the 40th number.
+fib(40)
+</pre></div>
+</div>
+<p>We also allow Kaleidoscope to call into standard library functions (the
+LLVM JIT makes this completely trivial). This means that you can use the
+‘extern’ keyword to define a function before you use it (this is also
+useful for mutually recursive functions). For example:</p>
+<div class="highlight-python"><div class="highlight"><pre>extern sin(arg);
+extern cos(arg);
+extern atan2(arg1 arg2);
+
+atan2(sin(.4), cos(42))
+</pre></div>
+</div>
+<p>A more interesting example is included in Chapter 6 where we write a
+little Kaleidoscope application that <a class="reference external" href="OCamlLangImpl6.html#example">displays a Mandelbrot
+Set</a> at various levels of magnification.</p>
+<p>Lets dive into the implementation of this language!</p>
+</div>
+<div class="section" id="the-lexer">
+<h2><a class="toc-backref" href="#id3">1.3. The Lexer</a><a class="headerlink" href="#the-lexer" title="Permalink to this headline">¶</a></h2>
+<p>When it comes to implementing a language, the first thing needed is the
+ability to process a text file and recognize what it says. The
+traditional way to do this is to use a
+“<a class="reference external" href="http://en.wikipedia.org/wiki/Lexical_analysis">lexer</a>” (aka
+‘scanner’) to break the input up into “tokens”. Each token returned by
+the lexer includes a token code and potentially some metadata (e.g. the
+numeric value of a number). First, we define the possibilities:</p>
+<div class="highlight-ocaml"><div class="highlight"><pre><span class="c">(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of</span>
+<span class="c"> * these others for known things. *)</span>
+<span class="k">type</span> <span class="n">token</span> <span class="o">=</span>
+  <span class="c">(* commands *)</span>
+  <span class="o">|</span> <span class="nc">Def</span> <span class="o">|</span> <span class="nc">Extern</span>
+
+  <span class="c">(* primary *)</span>
+  <span class="o">|</span> <span class="nc">Ident</span> <span class="k">of</span> <span class="kt">string</span> <span class="o">|</span> <span class="nc">Number</span> <span class="k">of</span> <span class="kt">float</span>
+
+  <span class="c">(* unknown *)</span>
+  <span class="o">|</span> <span class="nc">Kwd</span> <span class="k">of</span> <span class="kt">char</span>
+</pre></div>
+</div>
+<p>Each token returned by our lexer will be one of the token variant
+values. An unknown character like ‘+’ will be returned as
+<tt class="docutils literal"><span class="pre">Token.Kwd</span> <span class="pre">'+'</span></tt>. If the curr token is an identifier, the value will be
+<tt class="docutils literal"><span class="pre">Token.Ident</span> <span class="pre">s</span></tt>. If the current token is a numeric literal (like 1.0),
+the value will be <tt class="docutils literal"><span class="pre">Token.Number</span> <span class="pre">1.0</span></tt>.</p>
+<p>The actual implementation of the lexer is a collection of functions
+driven by a function named <tt class="docutils literal"><span class="pre">Lexer.lex</span></tt>. The <tt class="docutils literal"><span class="pre">Lexer.lex</span></tt> function is
+called to return the next token from standard input. We will use
+<a class="reference external" href="http://caml.inria.fr/pub/docs/manual-camlp4/index.html">Camlp4</a> to
+simplify the tokenization of the standard input. Its definition starts
+as:</p>
+<div class="highlight-ocaml"><div class="highlight"><pre><span class="c">(*===----------------------------------------------------------------------===</span>
+<span class="c"> * Lexer</span>
+<span class="c"> *===----------------------------------------------------------------------===*)</span>
+
+<span class="k">let</span> <span class="k">rec</span> <span class="n">lex</span> <span class="o">=</span> <span class="n">parser</span>
+  <span class="c">(* Skip any whitespace. *)</span>
+  <span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">' '</span> <span class="o">|</span> <span class="sc">'\n'</span> <span class="o">|</span> <span class="sc">'\r'</span> <span class="o">|</span> <span class="sc">'\t'</span><span class="o">);</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">lex</span> <span class="n">stream</span>
+</pre></div>
+</div>
+<p><tt class="docutils literal"><span class="pre">Lexer.lex</span></tt> works by recursing over a <tt class="docutils literal"><span class="pre">char</span> <span class="pre">Stream.t</span></tt> to read
+characters one at a time from the standard input. It eats them as it
+recognizes them and stores them in in a <tt class="docutils literal"><span class="pre">Token.token</span></tt> variant. The
+first thing that it has to do is ignore whitespace between tokens. This
+is accomplished with the recursive call above.</p>
+<p>The next thing <tt class="docutils literal"><span class="pre">Lexer.lex</span></tt> needs to do is recognize identifiers and
+specific keywords like “def”. Kaleidoscope does this with a pattern
+match and a helper function.</p>
+<div class="highlight-ocaml"><div class="highlight"><pre>  <span class="c">(* identifier: [a-zA-Z][a-zA-Z0-9] *)</span>
+  <span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">'A'</span> <span class="o">..</span> <span class="sc">'Z'</span> <span class="o">|</span> <span class="sc">'a'</span> <span class="o">..</span> <span class="sc">'z'</span> <span class="k">as</span> <span class="n">c</span><span class="o">);</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
+      <span class="k">let</span> <span class="n">buffer</span> <span class="o">=</span> <span class="nn">Buffer</span><span class="p">.</span><span class="n">create</span> <span class="mi">1</span> <span class="k">in</span>
+      <span class="nn">Buffer</span><span class="p">.</span><span class="n">add_char</span> <span class="n">buffer</span> <span class="n">c</span><span class="o">;</span>
+      <span class="n">lex_ident</span> <span class="n">buffer</span> <span class="n">stream</span>
+
+<span class="o">...</span>
+
+<span class="ow">and</span> <span class="n">lex_ident</span> <span class="n">buffer</span> <span class="o">=</span> <span class="n">parser</span>
+  <span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">'A'</span> <span class="o">..</span> <span class="sc">'Z'</span> <span class="o">|</span> <span class="sc">'a'</span> <span class="o">..</span> <span class="sc">'z'</span> <span class="o">|</span> <span class="sc">'0'</span> <span class="o">..</span> <span class="sc">'9'</span> <span class="k">as</span> <span class="n">c</span><span class="o">);</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
+      <span class="nn">Buffer</span><span class="p">.</span><span class="n">add_char</span> <span class="n">buffer</span> <span class="n">c</span><span class="o">;</span>
+      <span class="n">lex_ident</span> <span class="n">buffer</span> <span class="n">stream</span>
+  <span class="o">|</span> <span class="o">[<</span> <span class="n">stream</span><span class="o">=</span><span class="n">lex</span> <span class="o">>]</span> <span class="o">-></span>
+      <span class="k">match</span> <span class="nn">Buffer</span><span class="p">.</span><span class="n">contents</span> <span class="n">buffer</span> <span class="k">with</span>
+      <span class="o">|</span> <span class="s2">"def"</span> <span class="o">-></span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Def</span><span class="o">;</span> <span class="n">stream</span> <span class="o">>]</span>
+      <span class="o">|</span> <span class="s2">"extern"</span> <span class="o">-></span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Extern</span><span class="o">;</span> <span class="n">stream</span> <span class="o">>]</span>
+      <span class="o">|</span> <span class="n">id</span> <span class="o">-></span> <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Ident</span> <span class="n">id</span><span class="o">;</span> <span class="n">stream</span> <span class="o">>]</span>
+</pre></div>
+</div>
+<p>Numeric values are similar:</p>
+<div class="highlight-ocaml"><div class="highlight"><pre>  <span class="c">(* number: [0-9.]+ *)</span>
+  <span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">'0'</span> <span class="o">..</span> <span class="sc">'9'</span> <span class="k">as</span> <span class="n">c</span><span class="o">);</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
+      <span class="k">let</span> <span class="n">buffer</span> <span class="o">=</span> <span class="nn">Buffer</span><span class="p">.</span><span class="n">create</span> <span class="mi">1</span> <span class="k">in</span>
+      <span class="nn">Buffer</span><span class="p">.</span><span class="n">add_char</span> <span class="n">buffer</span> <span class="n">c</span><span class="o">;</span>
+      <span class="n">lex_number</span> <span class="n">buffer</span> <span class="n">stream</span>
+
+<span class="o">...</span>
+
+<span class="ow">and</span> <span class="n">lex_number</span> <span class="n">buffer</span> <span class="o">=</span> <span class="n">parser</span>
+  <span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">'0'</span> <span class="o">..</span> <span class="sc">'9'</span> <span class="o">|</span> <span class="sc">'.'</span> <span class="k">as</span> <span class="n">c</span><span class="o">);</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
+      <span class="nn">Buffer</span><span class="p">.</span><span class="n">add_char</span> <span class="n">buffer</span> <span class="n">c</span><span class="o">;</span>
+      <span class="n">lex_number</span> <span class="n">buffer</span> <span class="n">stream</span>
+  <span class="o">|</span> <span class="o">[<</span> <span class="n">stream</span><span class="o">=</span><span class="n">lex</span> <span class="o">>]</span> <span class="o">-></span>
+      <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Number</span> <span class="o">(</span><span class="n">float_of_string</span> <span class="o">(</span><span class="nn">Buffer</span><span class="p">.</span><span class="n">contents</span> <span class="n">buffer</span><span class="o">));</span> <span class="n">stream</span> <span class="o">>]</span>
+</pre></div>
+</div>
+<p>This is all pretty straight-forward code for processing input. When
+reading a numeric value from input, we use the ocaml <tt class="docutils literal"><span class="pre">float_of_string</span></tt>
+function to convert it to a numeric value that we store in
+<tt class="docutils literal"><span class="pre">Token.Number</span></tt>. Note that this isn’t doing sufficient error checking:
+it will raise <tt class="docutils literal"><span class="pre">Failure</span></tt> if the string “1.23.45.67”. Feel free to
+extend it :). Next we handle comments:</p>
+<div class="highlight-ocaml"><div class="highlight"><pre>  <span class="c">(* Comment until end of line. *)</span>
+  <span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">'#'</span><span class="o">);</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
+      <span class="n">lex_comment</span> <span class="n">stream</span>
+
+<span class="o">...</span>
+
+<span class="ow">and</span> <span class="n">lex_comment</span> <span class="o">=</span> <span class="n">parser</span>
+  <span class="o">|</span> <span class="o">[<</span> <span class="k">'</span> <span class="o">(</span><span class="sc">'\n'</span><span class="o">);</span> <span class="n">stream</span><span class="o">=</span><span class="n">lex</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">stream</span>
+  <span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="n">c</span><span class="o">;</span> <span class="n">e</span><span class="o">=</span><span class="n">lex_comment</span> <span class="o">>]</span> <span class="o">-></span> <span class="n">e</span>
+  <span class="o">|</span> <span class="o">[<</span> <span class="o">>]</span> <span class="o">-></span> <span class="o">[<</span> <span class="o">>]</span>
+</pre></div>
+</div>
+<p>We handle comments by skipping to the end of the line and then return
+the next token. Finally, if the input doesn’t match one of the above
+cases, it is either an operator character like ‘+’ or the end of the
+file. These are handled with this code:</p>
+<div class="highlight-ocaml"><div class="highlight"><pre><span class="c">(* Otherwise, just return the character as its ascii value. *)</span>
+<span class="o">|</span> <span class="o">[<</span> <span class="k">'</span><span class="n">c</span><span class="o">;</span> <span class="n">stream</span> <span class="o">>]</span> <span class="o">-></span>
+    <span class="o">[<</span> <span class="k">'</span><span class="nn">Token</span><span class="p">.</span><span class="nc">Kwd</span> <span class="n">c</span><span class="o">;</span> <span class="n">lex</span> <span class="n">stream</span> <span class="o">>]</span>
+
+<span class="c">(* end of stream. *)</span>
+<span class="o">|</span> <span class="o">[<</span> <span class="o">>]</span> <span class="o">-></span> <span class="o">[<</span> <span class="o">>]</span>
+</pre></div>
+</div>
+<p>With this, we have the complete lexer for the basic Kaleidoscope
+language (the <a class="reference external" href="OCamlLangImpl2.html#code">full code listing</a> for the
+Lexer is available in the <a class="reference external" href="OCamlLangImpl2.html">next chapter</a> of the
+tutorial). Next we’ll <a class="reference external" href="OCamlLangImpl2.html">build a simple parser that uses this to build an
+Abstract Syntax Tree</a>. When we have that, we’ll
+include a driver so that you can use the lexer and parser together.</p>
+<p><a class="reference external" href="OCamlLangImpl2.html">Next: Implementing a Parser and AST</a></p>
+</div>
+</div>
+
+
+          </div>
+      </div>
+      <div class="clearer"></div>
+    </div>
+    <div class="related">
+      <h3>Navigation</h3>
+      <ul>
+        <li class="right" style="margin-right: 10px">
+          <a href="../genindex.html" title="General Index"
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+             >next</a> |</li>
+        <li class="right" >
+          <a href="LangImpl9.html" title="9. Kaleidoscope: Conclusion and other useful LLVM tidbits"
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