[racket] Delimited continuations and parameters

Also, just in case it wasn't obvious all along, here's another one:

#lang racket

(require racket/control)

(define p (make-parameter 0))
(define r (make-parameter 0))

((λ (f)
   (parameterize ([p 2])
     (values
      (parameterize ([r 20])
        (f 0)))))
 (parameterize ([p 1])
   (reset
    (parameterize ([r 10])
      ((λ (x) (+ (p) (r)))
       (shift f f))))))

On Mon, May 14, 2012 at 9:21 PM, Matthew Flatt <mflatt at cs.utah.edu> wrote:
> At Mon, 14 May 2012 21:50:01 -0400, Asumu Takikawa wrote:
>> On 2012-05-14 19:00:49 -0600, Matthew Flatt wrote:
>> > In other words, every `parameterize' uses the same continuation mark,
>> > so that `(parameterize ([r 10]) ...)' associates the parameterization
>> > continuation mark with a single record that maps `r' to 10, `p' to 1,
>> > etc. The entire record is carried by the delimited continuation.
>>
>> Thanks Matthew and Ryan, that clears it up. OTOH, it does look like a
>> straightforward translation to continuation marks (or using
>> unstable/markparam as Ryan pointed out) doesn't get the 12 result
>> either.
>>
>> For example:
>>
>>   #lang racket
>>
>>   (require racket/control
>>            unstable/markparam)
>>
>>   (define p (mark-parameter))
>>   (define r (mark-parameter))
>>
>>   ((λ (f)
>>      (mark-parameterize ([p 2])
>>        (mark-parameterize ([r 20])
>>          (f 0))))
>>    (mark-parameterize ([p 1])
>>      (reset
>>       (mark-parameterize ([r 10])
>>         ((λ (x) (+ (mark-parameter-first p)
>>                    (mark-parameter-first r)))
>>          (shift f f))))))
>>
>> Will produce an error
>> +: expects type <number> as 1st argument, given: #f; other arguments were: 10
>>
>> > In the ICFP'07 paper on delimited continuations in Racket, we wrote (at
>> > the end of section 5) that we'd probably change `parameterize', but
>> > we've never gotten around to that change. Meanwhile, raw continuation
>> > marks (as modeled directly in that paper) essentially match the
>> > dynamic-binding form of Kiselyov et al.
>>
>> The raw continuation mark version gives essentially the same error as
>> above, maybe because call/cc and call/comp restore the marks to what was
>> present at capture time, which doesn't include the `p` mark?
>
> It's because `unstable/markparam' lookup is delimited by the default
> continuation prompt --- and I suppose that's a twist relative to
> Kiselyov et al. and another facet of `control'+`prompt' versus
> `shift'+`reset'. Below are two variants that produce 12.
>
> ----------------------------------------
>
> #lang racket
>
> (require racket/control)
>
> (define (get-mark key)
>  (continuation-mark-set-first #f
>                               key
>                               #f
>                               mark-prompt))
>
> (define mark-prompt (make-continuation-prompt-tag))
>
> (call-with-continuation-prompt
>  (lambda ()
>   ((λ (f)
>       (with-continuation-mark 'p 2
>         (with-continuation-mark 'r 20
>           (f 0))))
>    (with-continuation-mark 'p 1
>      (reset
>       (with-continuation-mark 'r 10
>         ((λ (x) (+ (get-mark 'p)
>                    (get-mark 'r)))
>          (shift f f)))))))
>  mark-prompt)
>
> ----------------------------------------
>
> #lang racket
>
> (require racket/control)
>
> (define (get-mark key)
>  (continuation-mark-set-first #f
>                               key))
>
> ((λ (f)
>    (with-continuation-mark 'p 2
>      (with-continuation-mark 'r 20
>        (f 0))))
>  (with-continuation-mark 'p 1
>   (prompt
>    (with-continuation-mark 'r 10
>      ((λ (x) (+ (get-mark 'p)
>                 (get-mark 'r)))
>       (control f f))))))
>
>
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