Re: call/cc does not return a value

[Damien Mattei]

hello Mikael,

you remark help because ,even if 'let' and 'let-syntax' seems
interchangeable here, there was indeed a problem with syntax....
i did not write myself the macro originally and when comparing with def.scm
that allow returning value from a function there was a difference, there
was no use of kwd and stx should be used in place of it and even more it
should be simply stx and not (syntax kwd) or (syntax stx) in the macro
definition, here is the final version of code:


(define-syntax for

  (lambda (stx)

    (syntax-case stx ()

      ((_ (init test incrmt) body ...)

       (with-syntax ((BREAK (datum->syntax stx 'break))
                     (CONTINUE (datum->syntax stx 'continue)))
     (syntax
      (call/cc
       (lambda (escape)
         (let ((BREAK escape))
           init
           (let loop ()
         (when test
           (call/cc
            (lambda (next)
              (let ((CONTINUE next))
            (let () ;; allow definitions
              body ...)))) ; end call/cc
           incrmt
           (loop))) ; end let loop
           ))))) ;; close with-syntax
       ))))

and the good result now with Guile and Racket (not yet modified Kawa):

scheme@(guile-user)> (for ((define i 0) (< i 5) (set! i (+ i 1))) (define x
7) (display i)  (newline) (when (= i 2) (break "finish")))
0
1
2
$1 = "finish"

thank for you help , without you i would not have look so closely to this
macro written many years ago and used in the Guile,Racket and Kawa version
of Scheme+...

Damien

On Fri, Sep 13, 2024 at 10:25 AM Mikael Djurfeldt <mikael@djurfeldt.com>
wrote:

> Hi Damien,
>
> Maybe I'm missing something, but shoudn't it be:
>
> (define-syntax for
>   (lambda (stx)
>     (syntax-case stx ()
>       ((kwd (init test incrmt) body ...)
>        (with-syntax ((BREAK (datum->syntax (syntax kwd) 'break))
>                      (CONTINUE (datum->syntax (syntax kwd) 'continue)))
>      (syntax
>       (call/cc
>        (lambda (escape)
>          (let ((BREAK escape))
>            init
>            (let loop ()
>          (when test
>            (call/cc
>             (lambda (next)
>               (let ((CONTINUE next))
>             (let () ;; allow definitions
>               body ...)))) ; end call/cc
>            incrmt
>            (loop))) ; end let loop
>            ))))) ;; close with-syntax
>        ))))
>
> ?
>
> On Fri, Sep 13, 2024 at 8:53 AM Damien Mattei <damien.mattei@gmail.com>
> wrote:
> >
> > hello,
> >
> > i believed call/cc allowed to return value but i have this macro and i
> can
> > use continuation, but the value is not passed to the continuation:
> >
> > (define-syntax for
> >    (lambda (stx)
> >      (syntax-case stx ()
> >        ((kwd (init test incrmt) body ...)
> >
> >         (with-syntax ((BREAK (datum->syntax (syntax kwd) 'break))
> >                       (CONTINUE (datum->syntax (syntax kwd) 'continue)))
> >
> >     (syntax
> >      (call/cc
> >       (lambda (escape)
> > (let-syntax ((BREAK (identifier-syntax (escape))))
> >   init
> >   (let loop ()
> >     (when test
> >       (call/cc
> > (lambda (next)
> >  (let-syntax ((CONTINUE (identifier-syntax (next))))
> >    (let () ;; allow definitions
> >      body ...)))) ; end call/cc
> >       incrmt
> >       (loop))) ; end let loop
> >   ))))) ;; close with-syntax
> > ))))
> >
> >
> > mattei@acer:~$ guile
> > GNU Guile 3.0.9
> > Copyright (C) 1995-2023 Free Software Foundation, Inc.
> >
> > Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
> > This program is free software, and you are welcome to redistribute it
> > under certain conditions; type `,show c' for details.
> >
> > Enter `,help' for help.
> > scheme@(guile-user)> (use-modules (Scheme+))
> > WARNING: (Scheme+): imported module (if-then-else) overrides core binding
> > `if'
> > WARNING: (Scheme+): imported module (when-unless) overrides core binding
> > `when'
> > WARNING: (Scheme+): imported module (when-unless) overrides core binding
> > `unless'
> >
> > scheme@(guile-user)> (for ((define i 0) (< i 5) (set! i (+ i 1)))
> (define x
> > 7) (display i)  (newline) (when (= i 2) (break "finish")))
> > 0
> > 1
> > 2
> >
> > here i should get "finish" at REPL but nothing happens?
> >
> > regards
>