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bug#14039: Bug in with-fluids semantics
From: |
Daniel Hartwig |
Subject: |
bug#14039: Bug in with-fluids semantics |
Date: |
Sat, 23 Mar 2013 22:51:05 +0800 |
On 23 March 2013 18:41, Stefan Israelsson Tampe <address@hidden> wrote:
> 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
>
What values do you expect from successive calls to K?
> 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.
K captures S, a fluid, along with the dynamic extent. There is only a
single dynamic extent to which K resumes, and only one value
associated to the fluid S within that. Subsequent calls to K do not
generate a new dynamic extent, so it makes sense that modifications to
the fluids value persist. This example behaives as expected according
to my understanding of fluids.
Am I missing something?