Path: utzoo!attcan!utgpu!watmath!iuvax!uxc.cso.uiuc.edu!tank!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.text
Subject: Re: LaTeX: defining macros with optional arguments?
Message-ID: <18799@mimsy.UUCP>
Date: 28 Jul 89 14:12:57 GMT
References: <1989Jul28.020403.15263@telotech.uucp>
Reply-To: chris@mimsy.umd.edu.UUCP (Chris Torek)
Distribution: na
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 43

In article <1989Jul28.020403.15263@telotech.uucp> bsa@telotech.uucp
(Brandon S. Allbery) writes:
>... I can't quite get a handle on what magic incantations one uses to
>trap * and optional arguments in LaTeX macros.

Stars are found with \@ifstar, and optional arguments with \@ifnextchar[;
some documentation for these can be found near line 1500 of latex.tex.
Essentially, one defines \foo as

	\def\foo{\@ifstar{\@starredfoo}{\@regularfoo}}

for starred things, and

	\def\bar{\@ifnextchar[{\@bar}{@bar[defaultarg]}

for things that have optional arguments with defaults.

>The manual doesn't go in-depth on hacking LaTeX,

latex.tex is actually more informative than {\em The \LaTeX book}.

>Can someone explain to me (in words of one syllable or less ;-) how one
>goes about processing *-commands and optional arguments in home-grown
>LaTeX macros?

Only a little of TeX can be explained this way :-) .  However, it is
worth noting here that in raw TeX, one can get funny characters into
macros in two ways: either set the \catcode of the characters to 11
(`letter'), or use something like

	\expandafter\def\csname w&e*i+r-d\endcsname{foo}

\csname ...\endcsname turns `...' into a control sequence regardless
of what is in the `...'.  The \expandafter makes TeX `pick up' the
\def, hold on to it, read the next token (\csname), expand it (gobbling
up the ...\endcsname), and then act on the \def.  \expandafter can
be very strange; see {\em The \TeX book}, in particular Appendix D.

LaTeX has some internal macros to `sanitise' these \csname tricks
(\@namedef, \@nameuse).
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris