From: Alan Mackenzie <acm@muc.de>
To: help-gnu-emacs@gnu.org
Subject: Re: Is it possible for a macro to expand to nothing?
Date: Mon, 23 Nov 2009 20:09:34 +0000 (UTC) [thread overview]
Message-ID: <heeq5u$2vpo$1@colin2.muc.de> (raw)
In-Reply-To: mailman.11352.1258997403.2239.help-gnu-emacs@gnu.org
Hi, Drew!
Drew Adams <drew.adams@oracle.com> wrote:
>> I think I want to be able to do this:
>> (defun foo ()
>> (setq bar 1)
>> (ifdef baz (setq bar 2)))
>> , and if baz is nil at compile time, this function should be
>> identical to
>> (defun foo ()
>> (setq bar 1))
> (defmacro titi (fn)
> `(defun ,fn ()
> (setq bar 1)
> ,@(ifdef baz '((setq bar 2))))))
> Assuming that ifdef returns nil if baz is nil, that should give you
> (defun foo () (setq bar 1)). If baz is not nil, it should give you
> this:
> (defun foo ()
> (setq bar 1)
> (setq bar 2))
> Or something like that.
Wow, you're a genius, Drew! It's a little bit ugly having to write a
defmacro around a defun, but only a very very little.
The way you've described actually looks fairly obviousi now, but these
things always do after somebody bright has just shown you them.
Thanks again!
--
Alan Mackenzie (Nuremberg, Germany).
next prev parent reply other threads:[~2009-11-23 20:09 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-23 14:56 Is it possible for a macro to expand to nothing? Alan Mackenzie
2009-11-23 16:03 ` Drew Adams
[not found] ` <mailman.11344.1258992201.2239.help-gnu-emacs@gnu.org>
2009-11-23 16:31 ` Alan Mackenzie
2009-11-23 17:29 ` Drew Adams
2009-11-23 18:33 ` Pascal J. Bourguignon
2009-11-23 18:51 ` Drew Adams
[not found] ` <mailman.11354.1259004470.2239.help-gnu-emacs@gnu.org>
2009-11-23 20:08 ` Pascal J. Bourguignon
2009-11-23 20:24 ` Alan Mackenzie
2009-11-23 22:09 ` Drew Adams
[not found] ` <mailman.11367.1259014174.2239.help-gnu-emacs@gnu.org>
2009-11-23 23:55 ` Pascal J. Bourguignon
2009-11-24 0:55 ` Alan Mackenzie
2009-11-24 9:42 ` Pascal J. Bourguignon
2009-11-24 10:45 ` Alan Mackenzie
2009-11-24 11:14 ` Pascal J. Bourguignon
2009-11-24 16:39 ` Alan Mackenzie
2009-11-24 19:17 ` Pascal J. Bourguignon
2009-11-25 14:13 ` Jeff Clough
[not found] ` <mailman.11467.1259158369.2239.help-gnu-emacs@gnu.org>
2009-11-26 6:53 ` Alan Mackenzie
2009-11-26 11:11 ` Pascal J. Bourguignon
2009-11-26 11:52 ` Lennart Borgman
[not found] ` <mailman.11564.1259236392.2239.help-gnu-emacs@gnu.org>
2009-11-26 12:16 ` Pascal J. Bourguignon
2009-11-26 12:43 ` Lennart Borgman
2009-11-27 8:32 ` Kevin Rodgers
[not found] ` <mailman.11626.1259310779.2239.help-gnu-emacs@gnu.org>
2009-11-27 13:15 ` Alan Mackenzie
2009-11-27 13:52 ` Pascal J. Bourguignon
2009-11-27 16:57 ` Alan Mackenzie
2009-11-27 17:09 ` Pascal J. Bourguignon
2009-11-27 17:19 ` Helmut Eller
2009-11-27 17:45 ` Pascal J. Bourguignon
2009-11-27 23:17 ` Tim X
2009-11-28 0:06 ` Pascal J. Bourguignon
2009-11-28 8:29 ` Alan Mackenzie
2009-11-28 10:25 ` Pascal J. Bourguignon
2009-11-28 12:57 ` Thierry Volpiatto
[not found] ` <mailman.11699.1259413441.2239.help-gnu-emacs@gnu.org>
2009-11-29 0:54 ` Pascal J. Bourguignon
2009-11-24 11:56 ` Pascal J. Bourguignon
[not found] ` <mailman.11352.1258997403.2239.help-gnu-emacs@gnu.org>
2009-11-23 18:42 ` Pascal J. Bourguignon
2009-11-23 20:12 ` Drew Adams
[not found] ` <mailman.11356.1259007263.2239.help-gnu-emacs@gnu.org>
2009-11-23 20:21 ` Pascal J. Bourguignon
2009-11-23 22:09 ` Drew Adams
[not found] ` <mailman.11368.1259014177.2239.help-gnu-emacs@gnu.org>
2009-11-24 0:03 ` Pascal J. Bourguignon
2009-11-23 20:09 ` Alan Mackenzie [this message]
2009-11-23 16:49 ` Jeff Clough
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