* bug#14859: my-or macro in documentation
@ 2013-07-13 18:52 Josep Portella Florit
2013-07-14 0:41 ` Mark H Weaver
0 siblings, 1 reply; 2+ messages in thread
From: Josep Portella Florit @ 2013-07-13 18:52 UTC (permalink / raw)
To: 14859
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
^ permalink raw reply [flat|nested] 2+ messages in thread* bug#14859: my-or macro in documentation 2013-07-13 18:52 bug#14859: my-or macro in documentation Josep Portella Florit @ 2013-07-14 0:41 ` Mark H Weaver 0 siblings, 0 replies; 2+ messages in thread From: Mark H Weaver @ 2013-07-14 0:41 UTC (permalink / raw) To: Josep Portella Florit; +Cc: 14859-done Hi! Josep Portella Florit <jpf@primfilat.com> 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 ^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2013-07-14 0:41 UTC | newest] Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2013-07-13 18:52 bug#14859: my-or macro in documentation Josep Portella Florit 2013-07-14 0:41 ` Mark H Weaver
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