How to make define a command that takes more than 9 arguments

Question

I have a mathematical transformation that takes 16 parameters (grouped into 3+8+5) and would like to make a latex command for it, so that I can easily change the notation for it if the need arises.

As far as I know, both \def and \newcommand take a maximum of 9 arguments, is there any (recommended) way to extend this?

Answer 1

You are going to have to parse the arguments some at a time and store them into temporary registers or macros. For example

\newcommand\foo[9]{%
    \def\tempa{#1}%
    \def\tempb{#2}%
    \def\tempc{#3}%
    \def\tempd{#4}%
    \def\tempe{#5}%
    \def\tempf{#6}%
    \def\tempg{#7}%
    \def\temph{#8}%
    \def\tempi{#9}%
    \foocontinued
}
\newcommand\foocontinued[7]{%
    % Do whatever you want with your 9+7 arguments here.
}

Answer 2

There's the xargs package, and there's also some black TeX magic. As for myself, being conditioned in Python, I prefer the key-value parameter syntax provided by keyval/xkeyval packages.

On an unrelated note, if I find myself needing more than 9 parameters, that usually means that my macro/def/code organization is not very good, and I'd try to improve that first. But of course, there are legitimate situations where 9 parameters are perfectly okay --- especially if you try to build a definition with a lot of knobs and tweaks.

Answer 3

In a response to How to use variables inside a command when generating a table? I mention how the stringstrings package has a \getargs command that will parse large numbers of arguments that are passed within a single { }. To recap that reply,

\documentclass{article}
\usepackage{stringstrings}
\begin{document}
\getargs{1 2 3 4 5 6 7 8 9 10 11 12 FinalArgument}
There are \narg~arguments.  The thirteenth is \argxiii
\end{document}

The result to this example is:

There are 13 arguments. The thirteenth is FinalArgument