Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!samsung!umich!vela!rjohnson
From: rjohnson@vela.acs.oakland.edu (R o d Johnson)
Newsgroups: comp.text.tex
Subject: Testing for null arguments
Keywords: latex
Message-ID: <5396@vela.acs.oakland.edu>
Date: 13 Mar 91 22:09:32 GMT
Organization: Storefront Witchdoctors
Lines: 35


This is undoubtedly a question with a simple answer that I just can't
seem to get. I want to have a macro (for use in LaTeX documents) that
can have three arguments, two of which can be null.  It's invoked like
this:

  \prt{arg1}{arg2}{arg3}

but could also look like any of the following:

  \prt{}{arg2}{arg3}
  \prt{arg1}{arg2}{}
  \prt{}{arg2}{}

(arg2 will always be present).  I want to define an new \if (I guess)
that would allow me to define a macro like the following:

  \def\part#1#2#3{%           % or should there be braces around
   [some code]                % the arguments in the definition?
  %
  \ifnull{#1} \relax \else    % I guess it would be simpler to have
   [some more code]           % an \ifnotnull to do this
  \fi
  %
  \ifnull{#3} \relax \else
   [some more code]
  \fi
  }

I just can't figure out how to come up with an \ifnull or \ifnotnull.
Any suggestions?  Thanks in advance.

-- 
 Rod Johnson  *  rjohnson@vela.acs.oakland.edu  *  (313) 650 2315 

                "Life has a throat" --Peter Blegvad