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 <shiro.ka...@gmail.com>:
>
> Racket v8.6 behaves the same way.
>
> On Fri, Nov 18, 2022 at 9:29 AM Shiro Kawai <shiro.ka...@gmail.com> wrote:
>>
>> I used Racket v7.2, and here's the full transcription. I'm going to check
>> with the newest Racket.
>>
>> shiro@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
>> <marc.nie...@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
>>> <shiro.ka...@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.
>>> >
>>> >
>>> >
>>> >
>>> >
>>> >
>>> >
