with-fluids bug?

with-fluids bug?

[Stefan Israelsson Tampe]

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Hi,

Here follows an issue with resent head and a potential first start
of a solution.

Problem:
(define a (make-fluid))
(with-fluids ((a 1)) 2)  ; returns 2
(pk (with-fluids ((a 1)) 2)) ; barfs at trying to execute function 1

The issue:
the wind-fluids instruction reads previouslyu pushed fluids and vals
and set their value acordingly. But does just do a read and no pop!
by simply adding sp -= 2*n, the code above works fine. 

Now, I'm not an expert at coding vm-instruction, there might be more to
say here but a patch follows this mail.

Regards
Stefan


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diff --git a/libguile/vm-i-system.c b/libguile/vm-i-system.c
index 05c632c..1c5cafb 100644
--- a/libguile/vm-i-system.c
+++ b/libguile/vm-i-system.c
@@ -1582,6 +1582,7 @@ VM_DEFINE_INSTRUCTION (90, wind_fluids, "wind-fluids", 1, -1, 0)
   wf = scm_i_make_with_fluids (n, sp + 1 - 2*n, sp + 1 - n);
   scm_i_swap_with_fluids (wf, dynstate);
   scm_i_set_dynwinds (scm_cons (wf, scm_i_dynwinds ()));
+  sp -= 2*n;
   NEXT;
 }
 

Re: with-fluids bug?

[Andy Wingo]

Hi,

On Sun 26 Sep 2010 22:44, Stefan Israelsson Tampe <stefan.tampe@spray.se> writes:

> Problem:
> (define a (make-fluid))
> (with-fluids ((a 1)) 2)  ; returns 2
> (pk (with-fluids ((a 1)) 2)) ; barfs at trying to execute function 1

Thank you for this bug report and patch :)

I have made an equivalent fix to yours, but more like the `vector'
instruction's approach to calling NULLSTACK and more uniform underflow
checking.

Thanks again!

Andy
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