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: Sat, 28 Nov 2009 08:29:12 +0000 (UTC) [thread overview]
Message-ID: <heqn0o$pn2$1@colin2.muc.de> (raw)
In-Reply-To: 87d4335x8t.fsf@galatea.local
Pascal J. Bourguignon <pjb@informatimago.com> wrote:
> Tim X <timx@nospam.dev.null> writes:
>> On the other hand, Alan's arguments also have merit. If a macro can be
>> useful in generating something other than a form that can be
>> evaluated, such as a data structure and can do so in a way that is
>> cleaner/simpler or just easier to understand than doing the same using
>> functions, then it would make sense. His examples from the C modes
>> seem to be a case in point.
> Perhaps Alan's problem with functions comes from the confusion between
> backquote and macros. Since backquote (and , and ,@) are often used in
> macros, some people believe they can be used only in macros, and that
> they ARE what macros are.
Er, do I actually have a problem with functions? But no, I don't suffer
that particular confusion between backquotes and macros, and have indeed
used backquote when there hasn't been a macro within zeptoparsecs.
> Far from it! I don't know any language more orthogonal than lisp.
Maybe not, but even lisp only gets to about 89 degrees. It is missing an
operator which does the same as ,@ outside backquote. This is one of the
lacks which makes it so difficult to write an equivalent of C's #if.
> Backquote can be used in a function to build a s-exp (including part of
> a form) as it can be used anywhere.
> Therefore it is really not easier to use macros to generate parts of a
> form than function.
It is if you need "side effects", like c-lang-defconst and friends do.
[ Stuff read and appreciated. My brain's not up to it so early in the
morning].
> If you wanted to use macros, in addition to the complexity of having
> to use macroexpand to use it, you would have the difficulty of passing
> the parameters, since a macro gets it's parameters from the source
> form. In the case of a function, you have the choice to quote or not
> to quote the parameters, with macros they're always quoted for you.
In the case of a function, you've GOT to quote, which can get very
tedious in some circumstances. That's probably the reason that Martin
Stjernholm wrote c-lang-const etc. as macros.
--
Alan Mackenzie (Nuremberg, Germany).
next prev parent reply other threads:[~2009-11-28 8:29 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 [this message]
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
2009-11-23 16:49 ` Jeff Clough
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