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From: hanche@imf.unit.no (Harald Hanche-Olsen)
Newsgroups: comp.text.tex
Subject: Re: simple tex/latex question/puzzler/quiz
Message-ID: <HANCHE.90Dec10190755@hufsa.imf.unit.no>
Date: 10 Dec 90 18:07:55 GMT
References: <4221@exodus.Eng.Sun.COM>
Sender: news@ugle.unit.no
Organization: The Norwegian Institute of Technology, Trondheim, Norway.
Lines: 62
In-Reply-To: rom@xor.Eng.Sun.COM's message of 10 Dec 90 06:37:54 GMT

In article <4221@exodus.Eng.Sun.COM> rom@xor.Eng.Sun.COM (Circuit Group) writes:

   I'm stuck; any help is welcome.
   -------------------------------------------
   \documentstyle{article}
   \begin{document}
   \def\macro1{apple}
   \def\macro2{\macro1}
   \ifx \macro1\macro2 truetext \else falsetext \fi
   macro1\macro1 end
   macro2\macro2 end
   some text here.
   \end{document}
   --------------------------------------------
   produces:
   falsetext
   macro1appleend macro2appleend
   some text here.
   -------------------------------------------

When I run this through LaTeX, I get

! Use of \macro doesn't match its definition.
l.6 macro1\macro1
                  end
? 

because Macro names are made up of letters only, no digits allowed.
So you first defined \macro in such a manner that it must always be
immediately followed by `1' when used, and then so it must be
immediately follwed by `2'.  Your \ifx line compared the meaning of
\macro with that of 1, and found them different.  Your usage of
\macro1 on line 6 is an error.

Now that that is out of the way, lets assume you had named your macros
\macroa and \macrob.  Now your example essentially does what you
described.

   It appears that \ifx is not expanding the macro \macro1, does this
   make sense?

Yes, \ifx only compares the immediate meaning of tokens, and for
macros that means comparing the immediate replacement text (and the
garbage, if any, conatining a description of parameters and text to be
matched).

   How can I get an if statement that expands macros until
   its just text? Am I doing this the wrong way?

\edef\1{\macroa}
\edef\2{\macrob}
\ifx \1\2 truetext \else falsetext \fi

will work.  Exercise 1:  Look up \edef in the TeXbook and figure out
why this works.  Exercise 2:  Why is it ok to have macros named \1 and
\2 when I just expalined above that macro names consist of letters
only?  The answer is in the TeXbook.

- Harald Hanche-Olsen <hanche@imf.unit.no>
  Division of Mathematical Sciences
  The Norwegian Institute of Technology
  N-7034 Trondheim, NORWAY