GNU bug report logs - #14039
Bug in with-fluids semantics

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Package: guile;

Reported by: Stefan Israelsson Tampe <stefan.itampe <at> gmail.com>

Date: Sat, 23 Mar 2013 10:51:01 UTC

Severity: normal

Done: Andy Wingo <wingo <at> pobox.com>

Bug is archived. No further changes may be made.

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From: Stefan Israelsson Tampe <stefan.itampe <at> gmail.com>
To: 14039 <at> debbugs.gnu.org
Subject: bug#14039: Bug in with-fluids semantics
Date: Sat, 23 Mar 2013 11:41:29 +0100

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
This bug report was last modified 12 years and 120 days ago.

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