# [racket] Multi-return Function Call

 From: Sam Tobin-Hochstadt (samth at ccs.neu.edu) Date: Tue Feb 21 08:45:06 EST 2012 Previous message: [racket] Multi-return Function Call Next message: [racket] Multi-return Function Call Messages sorted by: [date] [thread] [subject] [author]

That seems very surprising, since the journal paper (JFP 2006) about
MRLC talks a lot about implementation strategies, and includes
performance measurements for a compiler that implements MRLC.

I think Anthony's implementation resembles the implementation in terms
of exceptions discussed in section 11.1 of that paper.

On Tue, Feb 21, 2012 at 8:15 AM, J. Ian Johnson <ianj at ccs.neu.edu> wrote:
> I don't have the time right now to go through your implementation, but I will say that I've talked to Olin directly about implementing \lambda_{MR} and he answered that it he could not think of any good implementation story beyond interpretation.
>
> -Ian
> ----- Original Message -----
> From: "Anthony Carrico" <acarrico at memebeam.org>
> To: users at racket-lang.org
> Sent: Monday, February 20, 2012 8:21:06 PM GMT -05:00 US/Canada Eastern
> Subject: [racket] Multi-return Function Call
>
> It is only 60 LOC, so go ahead and take a look:
>  https://github.com/acarrico/multi
>
>
> AUTHOR: Anthony Carrico <acarrico at memebeam.org>
>
> This is an implementation of Olin Shivers'/David Fisher's
> "Multi-return Function Call". I'll quote from the abstract of their
> paper:
>
>  "It is possible to extend the basic notion of 'function call' to
>  allow functions to have multiple return points. This turns out to be
>  wide-ranging tour of such a feature..."
>
> The paper is at:
>  http://www.ccs.neu.edu/home/shivers/papers/mrlc.pdf
>
> I'm not aware of any published implementation of this feature. I wrote
> this version after looking at the language creation features in
> Racket. I was wondering how Racket might host languages with features
> that weren't supported by its primitives and multi came to mind, but
> after reading through the Racket documentation on continuations, I
> began to think that it was possible to implement multi as a plain old
> macro with continuation marks and prompts.
>
> My syntax has minor differences from the paper. Return points are
> indexed from ZERO, not one, since that is how vectors (etc.) are
> indexed in Scheme. Also, the indexed return point syntax isn't
> prefixed with #, and the lambda return point syntax doesn't have a
> lambda keyword.
>
> Look through test.rkt for a bunch of examples.
>
> ISSUES:
>
> I'd like to hear from someone who knows Racket really well to tell me
> if I'm barking up the wrong tree. Is there a better way to provide
> multi? Is what I have done reasonable?
>
> The macros could be better, and give better messages, etc. Please send
> a patch if you are good at that sort of thing.
>
> The multi macro would need to be improved to capture the super tail
> call semantics:
>  * A prompt should only be used when introducing lambda return points.
>  * Unused prompts could be popped off the "stack" before setting
>    up new return points.
>
> --
> Anthony Carrico
>
>
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--
sam th
samth at ccs.neu.edu



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