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bug#14039: Bug in with-fluids semantics
From: |
Stefan Israelsson Tampe |
Subject: |
bug#14039: Bug in with-fluids semantics |
Date: |
Sat, 23 Mar 2013 16:41:15 +0100 |
I would expect
(k) to be the same. Otherwise fluids would not mix well with undo redo sematics.
But I do understand that people might have decided that it should work
like this.
and knowing the this semantic, one can fix the problem. If the
semantics is correct
I really can't find an example where it is useful though. Do you have
an example?
/Stefan
On Sat, Mar 23, 2013 at 3:51 PM, Daniel Hartwig <address@hidden> wrote:
> 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?