The implementation looks good! It is indeed possible to implement ,\_MR via exceptions, local continuations, or prompts as Anthony has here. While I can't speak for Olin, I expect that his point is that implementing the transformations we discuss in the paper practically would require a (possibly byte-code) compiler that knew about multi-returns internally. I don't know Racket internals well enough to discuss prompts, but I imagine they don't allow the kinds of tail-call optimizations that such a compiler would. Dave <div class="gmail_quote">On Tue, Feb 21, 2012 at 9:32 AM, J. Ian Johnson <<a href="mailto:ianj@ccs.neu.edu">ianj@ccs.neu.edu</a>> wrote: <blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"> Perhaps I remembered wrong about interpretation, but I do know he said that he didn't have a good implementation story - he must not have been very satisfied with that journal article. <div class="im HOEnZb"> -Ian ----- Original Message ----- </div><div class="HOEnZb"><div class="h5">From: "Sam Tobin-Hochstadt" <<a href="mailto:samth@ccs.neu.edu">samth@ccs.neu.edu</a>> To: "J. Ian Johnson" <<a href="mailto:ianj@ccs.neu.edu">ianj@ccs.neu.edu</a>> Cc: "Anthony Carrico" <<a href="mailto:acarrico@memebeam.org">acarrico@memebeam.org</a>>, <a href="mailto:users@racket-lang.org">users@racket-lang.org</a> Sent: Tuesday, February 21, 2012 8:45:06 AM GMT -05:00 US/Canada Eastern Subject: Re: [racket] Multi-return Function Call 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 <<a href="mailto:ianj@ccs.neu.edu">ianj@ccs.neu.edu</a>> 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" <<a href="mailto:acarrico@memebeam.org">acarrico@memebeam.org</a>> > To: <a href="mailto:users@racket-lang.org">users@racket-lang.org</a> > 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: > <a href="https://github.com/acarrico/multi" target="_blank">https://github.com/acarrico/multi</a> > > README: > > AUTHOR: Anthony Carrico <<a href="mailto:acarrico@memebeam.org">acarrico@memebeam.org</a>> > > 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 > a surprisingly useful mechanism. This article conducts a fairly > wide-ranging tour of such a feature..." > > The paper is at: > <a href="http://www.ccs.neu.edu/home/shivers/papers/mrlc.pdf" target="_blank">http://www.ccs.neu.edu/home/shivers/papers/mrlc.pdf</a> > > 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 > > > ____________________ > Racket Users list: > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> > ____________________ > Racket Users list: > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> -- sam th <a href="mailto:samth@ccs.neu.edu">samth@ccs.neu.edu</a> ____________________ Racket Users list: <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> </div></div></blockquote></div>