From: Maxime Devos <maximedevos@telenet.be>
To: Damien Mattei <damien.mattei@gmail.com>,
Matt Wette <matt.wette@gmail.com>
Cc: guile-user <guile-user@gnu.org>
Subject: Re: Fwd: new function
Date: Tue, 21 Sep 2021 21:03:27 +0200 [thread overview]
Message-ID: <52130eefb713942a36aa5717ef4c916173567ce3.camel@telenet.be> (raw)
In-Reply-To: <CADEOadcb84OQxMRBPT6Bp9ejSB6MV6vs-wPs-Lqyvz10nhDRBg@mail.gmail.com>
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Damien Mattei schreef op di 21-09-2021 om 15:04 [+0200]:
> i have tested define-once
> http://www.gnu.org/software/guile/docs/master/guile.html/Top-Level.html
> (the defvar of Lisp)and idea are:
> -unfortunately it is considered by scheme as a define,so there is some
> context where it is not allowed in my code
> -seems to work fine at toplevel (as mentioned in doc) but strange behavior
> in a function, i did not understand really what happened but i got some
> #unspecified value.
>
> here are my test code:
> cheme@(guile-user)> (define (foo2)
> (define-once x 1)
> (if #t
> (let ()
> (define-once x 2)
> ;;(set! x 2)
> (display "x=")
> (display x)
> (newline))
> 'never)
> (display x)
> (newline))
Possibly you want (added a set? argument for demonstration):
(define (foo2 set?)
(define x) ; define an (undefined or unbound, not sure about terminology) variable
(if set?
(let ()
(set! x 2) ; change the value of x
(display "x=")
(display x)
(newline))
'never)
(display x)
(newline))
That should be portable and avoids global state.
scheme@(guile-user)> x
;;; <stdin>:20:0: warning: possibly unbound variable `x'
ice-9/boot-9.scm:1685:16: In procedure raise-exception:
Unbound variable: x
scheme@(guile-user) [1]> ,q
scheme@(guile-user) [1]> (foo2 #f)
#<unspecified> ; I expected an error as would result from ...
;; ... this ...
scheme@(guile-user)> (variable-ref (make-undefined-variable))
ice-9/boot-9.scm:1685:16: In procedure raise-exception:
In procedure variable-ref: Unbound variable: #<variable 7f6de46cde80 value: #<undefined>>
Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
scheme@(guile-user) [2]>
;; instead of #<unpecified> but whatever ...
scheme@(guile-user) [1]> (foo2 #t)
x=2
2
scheme@(guile-user) [1]> (foo2 #t)
x=2
2
scheme@(guile-user) [1]> (define x 3)
scheme@(guile-user) [1]> (foo2 #t)
x=2 ; foo2 doesn't use the global variable 'x'
2
scheme@(guile-user) [1]> x
$1 = 3
Does this seem reasonable to you?
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next prev parent reply other threads:[~2021-09-21 19:03 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CADEOadfF+rR=fW0fS-PkQkDN8EHFB1sJnkeePMJyc23m9shLgA@mail.gmail.com>
2021-09-19 9:18 ` Fwd: new function Damien Mattei
2021-09-19 10:38 ` Maxime Devos
2021-09-19 14:45 ` Matt Wette
2021-09-19 14:56 ` Maxime Devos
2021-09-21 13:04 ` Damien Mattei
2021-09-21 19:03 ` Maxime Devos [this message]
2021-09-22 7:52 ` Damien Mattei
2021-09-22 18:03 ` Maxime Devos
2021-09-22 19:12 ` Taylan Kammer
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