Am Fr., 18. Nov. 2022 um 22:12 Uhr schrieb Marc Nieper-Wißkirchen
<xxxxxx@gmail.com>:
>
> At first sight, Racket's behavior looks strange (tested with 8.2):
>
> This expression
>
> (let ((m (make-parameter 0))
>       (n (make-parameter 0)))
>   (define k
>     (parameterize ((m 1))
>       (call-with-continuation-prompt
>        (lambda ()
>          (parameterize ()
>            ((call-with-composable-continuation
>              (lambda (k)
>                (lambda () k)))))))))
>   (k (lambda () (values (m) (n)))))
>
> evaluates to the values 0 0.  The following expression, however,
>
> (let ((m (make-parameter 0))
>       (n (make-parameter 0)))
>   (define k
>     (parameterize ((m 1))
>       (call-with-continuation-prompt
>        (lambda ()
>          (parameterize ((n 1))
>            ((call-with-composable-continuation
>              (lambda (k)
>                (lambda () k)))))))))
>   (k (lambda () (values (m) (n)))))
>
> evaluates to the values 1 1.
>
> The only difference is that the inner parameterization is not trivial.
>
> It seems to be that each non-trivial parameterize installs a new
> continuation mark (holding the complete new parameterization).  This
> is captured by c-w-c-c.  However, when there is no non-trivial
> parameterize, no continuation mark about parameterizations is
> installed in the frames that are captured, and so reinstalling the
> delimited continuation does not restore the relevant continuation
> marks.
>
> Actually, this model happens to coincide with my wording in SRFI 226:
> "Conceptually, each continuation contains at least one otherwise
> inaccessible parameterization continuation mark, whose value is a
> parameterization. The parameterization of a continuation is the value
> of the most recent parameterization continuation mark in the
> continuation. The parameterization of the current continuation is the
> current parameterization. The (current) parameterization can
> conceptually be seen as part of the dynamic environment."
>
> If I take this seriously, my sample implementation has to be corrected.

PS I would like to hear some opinions about it.  I think the sample
implementation's behavior (namely, to record the current
parameterization and the current exception handler stack at each
prompt so that it will be captured) makes more sense than what I wrote
literally (and what is Racket's behavior).

>
> Am Fr., 18. Nov. 2022 um 20:57 Uhr schrieb Marc Nieper-Wißkirchen
> <xxxxxx@gmail.com>:
> >
> > Here is an example using only the primitives:
> >
> > (let ((m (make-parameter 0)))
> >   ((parameterize ((m 4))
> >      (call-with-continuation-prompt
> >       (lambda ()
> >         ((call-with-composable-continuation
> >           (lambda (k)
> >             (abort-current-continuation (default-continuation-prompt-tag)
> >               (lambda () k))))))))
> >    m))
> >
> > In Racket, it evaluates to 0 and not to 4.
> >
> > Am Fr., 18. Nov. 2022 um 20:51 Uhr schrieb Shiro Kawai <xxxxxx@gmail.com>:
> > >
> > > Racket v8.6 behaves the same way.
> > >
> > > On Fri, Nov 18, 2022 at 9:29 AM Shiro Kawai <xxxxxx@gmail.com> wrote:
> > >>
> > >> I used Racket v7.2, and here's the full transcription.  I'm going to check with the newest Racket.
> > >>
> > >> xxxxxx@scherzo:~/src/srfi-226$ racket
> > >> Welcome to Racket v7.2.
> > >> > (require racket/control)
> > >> > (define (print . xs) (for-each display xs) (newline))
> > >> > (define m (make-parameter 0))
> > >> > (define c #f)
> > >> > (define (foo)
> > >>     (parameterize ((m 1))
> > >>       (reset
> > >>        (print 'a: (m))
> > >>        (shift k (print 'b: (m)) (set! c k))
> > >>        (print 'c: (m)))))
> > >> > (define (bar)
> > >>     (parameterize ((m 2))
> > >>       (c #f)))
> > >> > (foo)
> > >> a:1
> > >> b:1
> > >> > (bar)
> > >> c:2
> > >>
> > >>
> > >> On Fri, Nov 18, 2022 at 9:26 AM Marc Nieper-Wißkirchen <xxxxxx@gmail.com> wrote:
> > >>>
> > >>> Thanks for the report, Shiro!
> > >>>
> > >>> I have to investigate Racket's behavior.  In 11.3.2 of the Racket
> > >>> reference, it says: "If a continuation is captured during the
> > >>> evaluation of parameterize, invoking the continuation effectively
> > >>> re-introduces the parameterization, since a parameterization is
> > >>> associated to a continuation via a continuation mark (see Continuation
> > >>> Marks) using a private key."  This seems to be consistent with SRFI
> > >>> 226 and its sample implementation, but not consistent with your Racket
> > >>> experiments.
> > >>>
> > >>> Am Fr., 18. Nov. 2022 um 20:07 Uhr schrieb Shiro Kawai <xxxxxx@gmail.com>:
> > >>> >
> > >>> > It seems that there's a disagreement in how a delimited continuation captures dynamic environment, between Racket and srfi-226.
> > >>> >
> > >>> > Suppose the following code:
> > >>> >
> > >>> > ```
> > >>> > (define (print . xs) (for-each display xs) (newline))
> > >>> >
> > >>> > (define m (make-parameter 0))
> > >>> >
> > >>> > (define c #f)
> > >>> >
> > >>> > (define (foo)
> > >>> >   (parameterize ((m 1))
> > >>> >     (reset
> > >>> >      (print 'a: (m))
> > >>> >      (shift k (print 'b: (m)) (set! c k))
> > >>> >      (print 'c: (m)))))
> > >>> >
> > >>> > (define (bar)
> > >>> >   (parameterize ((m 2))
> > >>> >     (c #f)))
> > >>> > ```
> > >>> >
> > >>> > With srfi-226 (using reset/shift as given in the srfi) reference implementation on Chez, I get this:
> > >>> >
> > >>> > ```
> > >>> > > (run foo)
> > >>> > a:1
> > >>> > b:1
> > >>> > > (run bar)
> > >>> > c:1
> > >>> > ```
> > >>> >
> > >>> > With Racket racket/control, I get this:
> > >>> >
> > >>> > ```
> > >>> > > (foo)
> > >>> > a:1
> > >>> > b:1
> > >>> > > (bar)
> > >>> > c:2
> > >>> > ```
> > >>> >
> > >>> > I'm switching Gauche's internals to srfi-226 based model, and I noticed the difference---the current released version of Gauche (relying on dynamic-wind to handle parameterization) works like Racket, while the srfi-226 based version (using dynamic env chain to keep parameters) works like srfi-226 reference implementation.
> > >>> >
> > >>> > I think srfi-226 behavior is more consistent (when the delimited continuation is invoked, it restores the dynamic environment of the continuation of reset), but is there a plausible explanation of Racket behavior?
> > >>> >
> > >>> > This difference actually caused a compatibility problem of an existing application so I want to understand it fully.
> > >>> >
> > >>> >
> > >>> >
> > >>> >
> > >>> >
> > >>> >
> > >>> >