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<head>
<title>UK TeX FAQ -- question label moren9</title>
</head><body>
<h3>How to break the 9-argument limit</h3>
<p/>If you think about it, you will realise that Knuth&rsquo;s command
definition syntax:
<blockquote>
<pre>
\def\blah#1#2 ... #9{&lt;macro body&gt;}
</pre>
</blockquote><p>
is intrinsically limited to just 9 arguments.  There&rsquo;s no direct way
round this: how would you express a 10th argument? &mdash; and ensure that
the syntax didn&rsquo;t gobble some other valid usage?
<p/>If you really must have more than 9 arguments, the way to go is:
<blockquote>
<pre>
\def\blah#1#2 ... #9{%
  \def\ArgI{{#1}}%
  \def\ArgII{{#2}}%
  ...
  \def\ArgIX{{#9}}%
  \BlahRelay
}
\def\BlahRelay#1#2#3{%
  % arguments 1-9 are now in
  %   \ArgI-\ArgIX
  % arguments 10-12 are in
  %   #1-#3
  &lt;macro body&gt;%
}
</pre>
</blockquote><p>
This technique is easily extendible by concert pianists of the TeX
keyboard, but is really hard to recommend.
<p/>LaTeX users have the small convenience of merely giving a number of
arguments in the <code>\</code><code>newcommand</code> that defines each part of the
relaying mechanism: Knuth&rsquo;s restriction applies to <code>\</code><code>newcommand</code>
just as it does to <code>\</code><code>def</code>.  However, LaTeX users also have the
way out of such barbarous command syntax: the <i>keyval</i>
package.  With <i>keyval</i>, and a bit of programming, one can
write really quite sophisticated commands, whose invocation might look
like:
<blockquote>
<pre>
\flowerinstance{species=Primula veris,
  family=Primulaceae,
  location=Coldham's Common,
  locationtype=Common grazing land,
  date=1995/04/24,
  numplants=50,
  soiltype=alkaline
}
</pre>
</blockquote><p>
The merit of such verbosity is that it is self-explanatory: the typist
doesn&rsquo;t have to remember that argument twelve is <code>soiltype</code>, and so
on: the commands may be copied from field notes quickly and
accurately.
<dl>
<dt><tt><i>keyval.sty</i></tt><dd>Distributed as part of <a href="ftp://cam.ctan.org/tex-archive/macros/latex/required/graphics.zip">macros/latex/required/graphics</a> (<a href="ftp://cam.ctan.org/tex-archive/macros/latex/required/graphics.tar.gz">gzipped tar</a>, <a href="http://www.tex.ac.uk/tex-archive/macros/latex/required/graphics/">browse</a>)
</dl>
<p/><p>This question on the Web: <a href="http://www.tex.ac.uk/cgi-bin/texfaq2html?label=moren9">http://www.tex.ac.uk/cgi-bin/texfaq2html?label=moren9</a>
</body>