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Subject: |
Bug in with-fluids semantics |
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Date: |
Sat, 23 Mar 2013 11:41:29 +0100 |
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User-agent: |
KMail/4.9.5 (Linux/3.5.0-26-generic; KDE/4.9.5; x86_64; ; ) |
Consider this simple exmple with fluids and reodos via propmts,
(define (f x)
(let ((s (make-fluid 0)))
(with-fluids ((s 0))
(let lp ((i 0))
(cond ((>= i 100) (fluid-ref s))
((= i 50) (abort-to-prompt 'tag) (lp (+ i 1)))
(else (fluid-set! s (+ (fluid-ref s) i))
(lp (+ i 1))))))))
(define k (call-with-prompt 'tag (lambda () (f 1)) (lambda (k . l)
k)))
Then we will get in guile-2.0 pretty resent git version
scheme@(guile-user)> (k)
$1 = 4900
scheme@(guile-user)> (k)
$2 = 8575
The reason is that when the with-fluid returns normally it does a full
swap. It should only do half a swap e.g. restore the old value of the
fluid and not store the current which is of non use because it can not
be reached anymore and it contaminates the continuation k.
/Stefan
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--- Begin Message ---
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Subject: |
Re: bug#14039: Bug in with-fluids semantics |
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Date: |
Sat, 23 Mar 2013 20:07:31 +0100 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.2 (gnu/linux) |
On Sat 23 Mar 2013 11:41, Stefan Israelsson Tampe <address@hidden> writes:
> The reason is that when the with-fluid returns normally it does a full
> swap. It should only do half a swap e.g. restore the old value of the
> fluid and not store the current which is of non use because it can not
> be reached anymore and it contaminates the continuation k.
That's not how fluids work, semantically: for better (I think) or for
worse (you think). We cannot change this.
A
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http://wingolog.org/
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