From: Damien Mattei <damien.mattei@gmail.com>
To: guile-user@gnu.org
Subject: Re: escaping from a recursive call
Date: Thu, 10 Nov 2022 14:48:59 +0100 [thread overview]
Message-ID: <CADEOadcxmA9XKKMqSbU=KcpcT5+BrHxe6TQ_XEAW4DDLTR43uw@mail.gmail.com> (raw)
In-Reply-To: <20221110123244.af0bdfe7bb0ed55f9b761dff@gmail.com>
solutions have been posted, i'm using mine, which update my 'def macro:
;; (def (bar n);; (cond ((= n 0) 'end0);; ((= n 7)
(return-rec 'end7));; (else (cons n (bar {n - 1})))))
;; scheme@(guile-user)> (bar 5);; $4 = (5 4 3 2 1 . end0);;
scheme@(guile-user)> (bar 10);; $5 = end7
(define-syntax def
(lambda (stx)
(syntax-case stx ()
;; multiple definitions without values assigned
;; (def (x y z))
((_ (var1 ...)) #`(begin (define var1 '()) ...))
;; (def (foo) (when #t (return "hello") "bye"))
;; ((_ (<name> <arg> ...) <body> <body>* ...)
;; (let ((ret-id (datum->syntax stx 'return)))
;; #`(define (<name> <arg> ...)
;; (call/cc (lambda (#,ret-id) <body> <body>* ...)))))
((_ (<name> <arg> ...) <body> <body>* ...)
(let ((ret-id (datum->syntax stx 'return))
(ret-rec-id (datum->syntax stx 'return-rec)))
#`(define (<name> <arg> ...)
(call/cc (lambda (#,ret-rec-id)
(apply (rec <name> (lambda (<arg> ...)
(call/cc (lambda (#,ret-id) <body> <body>* ...)))) (list
<arg> ...)))))))
;; single definition without a value assigned
;; (def x)
((_ var) #`(define var '()))
;; (def x 7)
((_ var expr) #`(define var expr))
((_ err ...) #`(syntax-error "Bad def form"))
)))
i have tested it with my code and it works well,for now.
Also i can not notice any slowing of the code and that is important ad 'def
is a replacement often used in my projects now.
I will update my Scheme+ with it soon, when i have time.
Regards,
Damien
On Thu, Nov 10, 2022 at 1:33 PM Chris Vine <vine.chris@gmail.com> wrote:
> On Wed, 09 Nov 2022 12:55:42 -0500
> Olivier Dion via General Guile related discussions <guile-user@gnu.org>
> wrote:
> > On Wed, 09 Nov 2022, Damien Mattei <damien.mattei@gmail.com> wrote:
> > > but in the general case , i want a macro that can do it on any
> function
> > > (i'm not sure it can be done because the continuation have to be
> captured
> > > just before the call to the function and be inlined at the good
> > > place....)
> >
> > I'm not aware of any control mechanism that are implicit in Guile. You
> > almost always have to deal with a continuation object. However, nothing
> > prevent you to invent your own control flow wrapper.
>
> You can construct an anaphoric macro with that in mind. This introduces
> an imperative-style 'loop' macro which carries within the loop block a
> 'break' keyword which will cause the loop to exit:
>
> (use-modules (ice-9 control)) ;; for call/ec
>
> (define-syntax loop
> (lambda (x)
> (syntax-case x ()
> [(k e ...)
> (with-syntax ([break (datum->syntax #'k 'break)])
> #'(call/ec
> (lambda (break)
> (let f () e ... (f)))))])))
>
> (display (let ([n 3] [lst '()])
> (loop
> (if (= n 0) (break lst))
> (set! lst (cons 'a lst))
> (set! n (- n 1)))))
> (newline)
>
> However explicit control of loops is better in my view. Imperative
> loops usually end up with mutable bindings, as in the example above.
>
>
next prev parent reply other threads:[~2022-11-10 13:48 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-09 15:56 escaping from a recursive call Damien Mattei
2022-11-09 16:51 ` Olivier Dion via General Guile related discussions
2022-11-09 17:18 ` Damien Mattei
2022-11-09 17:55 ` Olivier Dion via General Guile related discussions
2022-11-09 18:49 ` Damien Mattei
2022-11-10 1:20 ` Olivier Dion via General Guile related discussions
2022-11-10 4:56 ` tomas
2022-11-10 6:01 ` Damien Mattei
2022-11-10 5:25 ` Damien Mattei
2022-11-10 17:03 ` Olivier Dion via General Guile related discussions
2022-11-10 12:32 ` Chris Vine
2022-11-10 13:48 ` Damien Mattei [this message]
2022-11-09 18:56 ` Zelphir Kaltstahl
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