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From: em@dce.ie (Eamonn McManus)
Newsgroups: comp.text.tex
Subject: Re: Testing for null arguments
Message-ID: <contentfreegrammar@dce.ie>
Date: 14 Mar 91 22:03:20 GMT
References: <5396@vela.acs.oakland.edu> <68473@brunix.UUCP>
Organization: Datacode Communications Ltd, Dublin, Ireland
Lines: 23

gvr@cs.brown.edu (George V. Reilly) writes:
>\def\part#1#2#3{%
>    \def\first{#1}	% Or something with more mnemonic value
>    \def\third{#1}
>    [some code]
>    %
>    \ifx\first\empty
>	% do nothing
>    \else
>	[some more code]
>    \fi

Another way of testing for null arguments is exemplified by this macro:
    \def\showempty#1{\message{\ifx\relax#1\relax empty\else not empty\fi}}

This has the advantage that it can be done entirely in TeX's mouth,
whereas the \def's in Geo's solution cannot.  It does however fail badly
if #1 begins with \relax (e.g., \showempty{\relax...}).

I have the feeling that there is a better solution.

,
Eamonn