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To: l...@toetsch.at
Cc: perl6-intern...@perl.org
Subject: Re: Continuations (again)
References: <m2znaata3d.fsf@obelisk.bofh.org.uk>
	<200403211747.i2LHlAg26610@thu8.leo.home>
Date: Sun, 21 Mar 2004 20:47:02 +0000
In-Reply-To: <200403211747.i2LHlAg26610@thu8.leo.home> (Leopold Toetsch's
 message of "Sun, 21 Mar 2004 18:47:10 +0100")
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From: pdcaw...@bofh.org.uk (Piers Cawley)

Leopold Toetsch <l...@toetsch.at> writes:

> Piers Cawley <pdcaw...@bofh.org.uk> wrote:
>> So, I'm trying to get my head 'round parrot's continuations. It's my
>> understanding that, at creation time, a Continuation closes over the
>> current user stacks, control stack and lexical pad (and possibly some
>> other stuff but those'll do for now).
>
> Yes register stacks. Which is one problem of your code. The calling
> sequence has a "savetop" inside, which isn't in the Continuations
> context.

But why do I need the savetop? I only care about the

>
> I already posted an working example.
> Here is another one (comments indicate problems with your code:
>
> .sub main
>     $P0 = new PerlUndef
>     $P0 = "Howdy, world\n"
>     save $P0
>     # create continuation inside, so that it has this in context
>     savetop
>     $P1 = newcont after
>     P5 = $P1
>     P0 = find_global "_invoker"
>     invokecc
> after:
>     restoretop
>     restore $P2
>     print $P2
>
>     end
>     # end *is* needed in main
> .end
>
> .sub _invoker
> #    ^^ global labels have an underscore
>     .param pmc a_cont
>     invoke a_cont
> .end
>
>> Weird hunh?
>
> As long as no one really can tell the semantics of Continuations, they
> have to be hand-crafted like above.

So why does the generated pasm work where the PIR doesn't? 

I can see why saving P0-2 would be a good idea, but after doesn't need
any of the other registers.