[racket] Delimited continuations and parameters

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))))))