Re: CPS != call/cc

[Dan Sugalski <address@hidden>]

At 8:00 AM -0400 8/7/03, John Clements wrote:
>On Wednesday, August 6, 2003, at 08:01  PM, Dan Sugalski wrote:
>
>>At 1:10 PM -0400 8/6/03, John Clements wrote:
>>>On Wednesday, August 6, 2003, at 11:00  AM, Peter J. Wasilko, Esq. wrote:
>>>
>>>>>Well... it can sort of help, but there are some limits. Multiple
>>>>>stacks tend to solve other problems, and they're certainly useful,
>>>>>but for a CPS scheme you really need more of a linked frame system
>>>>>than a stack system, since the control information really builds up a
>>>>>tree (albeit one often with a single branch) rather than a stack.
>>>>
>>>>Dan,
>>>>
>>>>     I see, so what would an optimal hardware architecture be for
>>>>supporting CPS?
>>>
>>>CPS, or continuation-passing-style, is not the same thing as a 
>>>language that includes primitives for continuations.
>>
>>While true, the threads are all in the context of Parrot, so its 
>>all semantics and no language. (Well, unless you consider assembly 
>>a language, but that's stretching things a bit) The continuations 
>>we use as part of the CPS scheme are all first class 
>>continuations--the only difference between them and first class 
>>continuations you make explicitly is that sometimes you don't have 
>>to explicitly make them.
>
>... and that's a HUGE difference. A difference in expressiveness.

No, actually, it isn't.

>All I'm saying is this: don't give another meaning to the 
>well-defined term CPS by using it to refer to any program that 
>captures continuations with call/cc or other similar primitives. 
>That's not what it means.

I think perhaps you're insufficiently familiar with part of the topic 
at hand (parrot) to say that for sure. Parrot *does* use CPS, and the 
continuations it uses are, for a variety of reasons, first-class 
continuations no different than you'd get if you took a continuation 
in a language. (How you got that continuation, via call/cc or 
explicit continuation creation, is irrelevant here)
-- 
                                         Dan

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Dan Sugalski                          even samurai
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