[cfe-commits] [PATCH] Implements hasAncestor.

[Sean Silva]

If you weren't aware of this (I wasn't until a couple days ago), there
is actually a whole subfield of computer science dedicated to pattern
matching. You may find some big inspiration by browsing the
literature.

I mention this because I recently stumbled upon the existence of this
subfield in the context of the Mathematica programming language, and
this hasAncestor match is extremely similar to something that happens
in the Mathematica programming language when an "upvalue" is matched,
although upvalues are much more general. In Mathematica, for example,
you can do:

g /: g[x_] + g[y_] := gplus[x, y]

which roughly means "whenever you see `g` as you traverse the
expression tree, check if the expression tree structure surrounding it
looks like g[<arbitrary expression to be bound to `x`>] + g[<arbitrary
expression to be bound to `y`>], and if it does, then rewrite that
subtree to be `gplus[x,y]`". The behavior needed to perform such
matching efficiently seems to be highly relevant to hasAncestor.

--Sean Silva

On Wed, Sep 5, 2012 at 9:53 AM, Manuel Klimek
<reviews at llvm-reviews.chandlerc.com> wrote:
> Hi djasper, mdiamond,
>
> A first shot at implementing the hasAncestor matcher. This builds
> on the previous patch that introduced DynTypedNode to build up
> a parent map for an dditional degree of freedom in the AST traversal.
>
> The map is only built once we hit an hasAncestor matcher, in order
> to not slow down matching for cases where this is not needed.
>
> We could implement some speed-ups for special cases, like building up
> the parent map as we go and only building up the full map if we break
> out of the already visited part of the tree, but that is probably
> not going to be worth it, and would make the code significantly more
> complex.
>
> http://llvm-reviews.chandlerc.com/D36
>
> Files:
>   include/clang/ASTMatchers/ASTMatchers.h
>   include/clang/ASTMatchers/ASTMatchersInternal.h
>   include/clang/ASTMatchers/ASTTypeTraits.h
>   lib/ASTMatchers/ASTMatchFinder.cpp
>   unittests/ASTMatchers/ASTMatchersTest.cpp
>
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