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Subject: |
my-or macro in documentation |
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Date: |
Sat, 13 Jul 2013 20:52:45 +0200 |
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User-agent: |
Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130623 Thunderbird/17.0.7 |
Hi!
The my-or example macro in the documentation has a subtle bug.
(letrec-syntax ((my-or
(syntax-rules ()
((my-or)
#t)
((my-or exp)
exp)
((my-or exp rest ...)
(let ((t exp))
(if exp
exp
(my-or rest ...)))))))
(my-or #f "rockaway beach"))
In the third rule t is bound to exp, presumably to use t instead of exp
to prevent evaluating exp multiple times, but t is never used and exp is
used again. This is the bug in action:
scheme@(guile-user)> (letrec-syntax ((my-or
(syntax-rules ()
((my-or)
#t)
((my-or exp)
exp)
((my-or exp rest ...)
(let ((t exp))
(if exp
exp
(my-or rest ...)))))))
(my-or (display "*") 1))
***scheme@(guile-user)>
I'm sure you already know how to fix it :-)
(letrec-syntax ((my-or
(syntax-rules ()
((my-or)
#t)
((my-or exp)
exp)
((my-or exp rest ...)
(let ((t exp))
(if t
t
(my-or rest ...)))))))
(my-or #f "rockaway beach"))
Josep
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--- Begin Message ---
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Subject: |
Re: bug#14859: my-or macro in documentation |
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Date: |
Sat, 13 Jul 2013 20:41:24 -0400 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) |
Hi!
Josep Portella Florit <address@hidden> writes:
> The my-or example macro in the documentation has a subtle bug.
>
> (letrec-syntax ((my-or
> (syntax-rules ()
> ((my-or)
> #t)
> ((my-or exp)
> exp)
> ((my-or exp rest ...)
> (let ((t exp))
> (if exp
> exp
> (my-or rest ...)))))))
> (my-or #f "rockaway beach"))
>
> In the third rule t is bound to exp, presumably to use t instead of exp
> to prevent evaluating exp multiple times, but t is never used and exp is
> used again.
Indeed! This was reported shortly after the 2.0.9 release, and has been
fixed in the stable-2.0 branch.
http://bugs.gnu.org/14203
http://git.savannah.gnu.org/gitweb/?p=guile.git;a=commitdiff;h=e006d87ba5942b6e49b39b951413dfe63785a398
Thanks!
Mark
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