[LLVMdev] Implementing closures and continuations

[Daniel Albuschat]

2013/6/30 David Farler <accumulator at icloud.com>

>
>
> On Jun 29, 2013, at 9:53 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
>
> On Sat, Jun 29, 2013 at 7:51 PM, David Farler <accumulator at icloud.com>wrote:
>
>> Hi all,
>>
>> In getting to know the LLVM infrastructure, I'm having a hard time
>> finding implementation details for closures and continuations.
>>
>> For closures, I've read comments such as "using a struct" as an
>> environment to hold references to free variables, linked lists to
>> dictionaries for various scope levels, and even things like "it's just like
>> virtual methods". I have a couple of questions regarding codegen,
>> especially in the context of a Lispy/Haskell-like language with automatic
>> reference counting of immutable objects allocated on the heap.
>>
>> What needs to be added to Functions during code generation? Is it a
>> really just a struct only holding offsets to free variables? Or do symbols
>> need to be looked up a kind of scope chain at runtime?
>>
>> Does adding a JIT complicate codegen of closures in terms of symbol
>> lookup in the bundled environment?
>>
>> Any recommendations for treating functions with no free variables vs
>> closures?
>>
>> Does implementing continuations greatly affect implementations of
>> closures? I assume the stack would need to be heap-allocated explicitly,
>> which might affect how pointers would be saved in a bundled environment.
>>
>
> Please read http://llvm.org/docs/tutorial/index.html .  I'm having
> trouble coming up with answers to most of your questions.
>
> If you need completely general continuations, yes, you'll want to
> explicitly allocate your stack.
>
> -Eli
>
>
> Thanks, this is the tutorial I've been reading and it's a great resource.
> I think I just need to start looking at some languages that already
> implement this. I can see now that free variable addresses are known at
> compile time and can be used in the future provided they are allocated on
> or moved to the heap.
>
> Still wondering about how to pack the structs and how eval/JIT affects
> this; I'll keep looking.
>

Hello David,

is your project somewhere up on github or so?
I'm implementing something that is relatively similar (at this point), so
it would be nice if I could have a look at your code.
As I'm still in the "learning LLVM IR"-phase, I have not much code put up,
but if you like I can post it as soon as something is available.

Greetings,
Daniel Albuschat
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