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From: ASND@TRIUMFCL.BITNET (Donald Arseneau)
Newsgroups: comp.text.tex
Subject: "Indirect" definitions in TeX
Message-ID: <3ABAC1810600429C@Post-Office.UH.EDU>
Date: 9 Mar 91 07:52:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 34

Malcolm Beattie writes:
>    I would like to be able to do something like:
>    ...
>    \define\makemark#1{\define\label#1{\the\chap.\the\sect}}
>    ...
>    \makemark{fred}       % Here, e.g. \chap = 6 and \sect = 7
>    ...
>    Of course, this doesn't work because the #1 in \define\label#1
>    doesn't get replaced by \makemark's first parameter, but instead
>    gets interpreted as a new local parameter for \label itself.
 
Actually, it gets interpreted as part of the SYNTAX for \label;
\makemark{fred} redefines \label as if you typed \define\label fred{...
when what you want is \define\labelfred.  This happens because the
command name is tokenized when it is first read in, not when #1 gets
processed.
 
The soultion is to use \csname to create the right commandname;
but take care not to redefine \csname itself!  :
 
\define\makemark#1{\expandafter\define\csname label#1\endcsname{...
 
I left out the definition because I suspect that what Malcolm tried
won't work as expected.  We need to expand \the\chap.\the\sect when
\makemark is performed, not when the \labelfred is used.
 
I don't really know what \define in AMS-TeX does; maybe it is equivalent
to TeX's \edef, which is what we really want! but I suspect it does a
normal \def, which would cause \labelfred to always report the current
section, not the correct cross reference.  Thus, I would use:
 
\def\makemark#1{\expandafter\edef\csname label#1\endcsname{\the\chap.\the\sect}}
 
Donald Arseneau                      asnd@triumfcl.bitnet