GNU bug report logs - #67669
29.1; Drop text suggesting using `and' to replace `if'

Previous Next

Full log

View this message in rfc822 format

From: Eli Zaretskii <eliz <at> gnu.org>
To: Xiyue Deng <manphiz <at> gmail.com>
Cc: 67669 <at> debbugs.gnu.org
Subject: bug#67669: 29.1; Drop text suggesting using `and' to replace `if'
Date: Fri, 08 Dec 2023 08:25:16 +0200

> From: Xiyue Deng <manphiz <at> gmail.com>
> Cc: 67669-done <at> debbugs.gnu.org
> Date: Thu, 07 Dec 2023 12:37:58 -0800
> 
> Eli Zaretskii <eliz <at> gnu.org> writes:
> 
> >> I was referring to whether we care about and use the result of the
> >> statement/function call.  In `and' we do, in `if' we don't and we just
> >> use the side effect.
> >
> > But that's not true.  'if' does return a value, and we do use it.
> > Consider this random example:
> >
> >   (defsubst posn-area (position)
> >     [...]
> >     (let ((area (if (consp (nth 1 position))
> > 		    (car (nth 1 position))
> > 		  (nth 1 position))))
> >       (and (symbolp area) area)))
> >
> > Here we bind 'area' to the value returned by 'if'.
> 
> Well if we use `if' with else then yes.

No.  When 'if' has no 'else' clause, and the test fails, 'if' returns
nil.  This is used in many places in our code.  Like this:

  (let (baz)
    (setq foo (concat "bar" (if (stringp baz) baz))))
    => "bar"

Here 'if' returns nil, and we use the feature of 'concat' to ignore
nil arguments.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.