[plt-scheme] call/cc, set!, and fluid-let

Well, there was a reason the post was off list. When I had a
persuasive case I planned on coming on list.

Thanks for the comments.

Jay

On 6/15/05, Matthias Felleisen <matthias at ccs.neu.edu> wrote:
> 
> On Jun 15, 2005, at 9:47 AM, Jay McCarthy wrote:
> 
> >   For list-related administrative tasks:
> >   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> >
> > On 6/15/05, John Clements <clements at brinckerhoff.org> wrote:
> >
> >> Taking this back to the list, hope that's okay.
> >>
> >> After thinking about this for a bit, I see two things:
> >>
> >> 1) I can just about imagine a situation like this where you want a
> >> change to be "permanent" for the rest of the computation but to be
> >> unwound when you hit the back button.
> >
> > That's the ticket.
> >
> >> 2) I don't understand why you need a thing like this for the situation
> >> you're describing.  I think I would just use a tail-call. Here's how I
> >> would structure the code, if I understand you correctly:
> >>
> >> (define (sorting-proc-a l) ...)
> >> (define (sorting-proc-b l) ...)
> >> (define (sorting-proc-c l) ...)
> >>
> >> (define (show-list l)
> >>    (send-suspend/callback-thingy (make-page l)
> >>       ; if user clicks "sort a":
> >>       => (show-list (sorting-proc-a l))
> >>       ; if user clicks "sort b":
> >>       => (show-list (sorting-proc-b l))
> >>       ; if user clicks "sort c":
> >>       => (show-list (sorting-proc-c l))
> >>       ; if user clicks something else:
> >>       => (call-to-somewhere-else ...)))
> >
> > Add to this example that reclicking "sort a" goes in reverse, and that
> > clicking "sort a", "sort b" causes the list to be sorted by b with a
> > as the tie breaker. See how the code needs future-of-the-computation
> > state.
> 
> If you want things unwound, you don't want explicit state. Instead, you
> want to pass around the values in a store-passing sense. So I am with
> Eli and John until you show me more.
> 
> -- Matthias (who suggested fluid-let as a session equivalent to SK)
> 
> 


-- 
Jay McCarthy <jay at cs.brown.edu>
http://jay.makeoutcity.com/