Subject: my-or macro in documentation
From: Josep Portella Florit <[email-masked]>
To: [email-masked]
Date: Sat, 13 Jul 2013 20:52:45 +0200
List-Id: <debbugs-submit.debbugs.gnu.org>

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