Simpler input for newcommand with many arguments

listofitemsmacros

I have a mathematical symbol with 6 labels but there are multiple conventions for displaying such a symbol. One way would be [F^{abc}_d]_{ef} but other people use, e.g., [F^{abc}_d]^{e}_{f} or other forms. Since I'm at the start of writing a thesis I'd prefer not to make an absolute choice and decided to define a command with 6 labels as input such as

\newcommand{\F}[6]{[F^{{#1} {#2} {#3}}_{#4}]^{#5}_{#6}}

but then I have to type \F{a}{b}{c}{d}{e}{f} which is a bit cumbersome. Is there any way that I could call the new command using a comma separated list, e.g. \F{a,b,c,d,e,f}, instead of the standard way??

Best Answer

The listofitems package can parse lists, using a comma (default) or other designated tokens.

Note that your list will need at least 5 commas, or an error will occur when calling \Fvar[6].

\documentclass{article}
\usepackage{listofitems}
\newcommand{\F}[1]{%
  \readlist*\Fvar{#1}%
  [F^{{\Fvar[1]} {\Fvar[2]} {\Fvar[3]}}_{\Fvar[4]}]^{\Fvar[5]}_{\Fvar[6]}}
\begin{document}
\begin{equation}
\F{a,b,c,d,e,f}
\end{equation}
\end{document}

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I have not progressed to the level of processing a list myself but I have been using etoolbox by Philipp Lehman for some other TeX programming tasks I am doing. I believe 3.7 List processing should give you a good solution.

For example (on a recent version of etoolbox) you can write:

\DeclareListParser*{\myfor}{;}
\myfor{\fbox}{item1; item2; item3}

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The xparse package has been mentioned in other answers. This offers a generic way to define (LaTeX2e-like) document commands without programming. There are a few ways you could implement what you want. One way is

\documentclass{article}

\usepackage{xparse}
\NewDocumentCommand{\dddfrac}{mG{}g}{%
  \IfNoValueTF{#3}
    {%
      \frac
        {\partial #2}
        {\partial #1}%
    }    
    {%
      \left (
      \frac{\partial #2}{\partial #1}
      \right )
      _{#3}
    }%
}

\begin{document}
$\dddfrac{x}$

$\dddfrac{y}{f_y}$

$\dddfrac{y}{f_y}{n}$
\end{document}

This sets up \dddfrac to require one mandatory argument (#1) and two arguments which are 'optional groups'. The first is set up with G{}, which means the default value is nothing at all. The second is set up as g, which will return a special marker \NoValue if it is not given. I use that to test for the last argument, which can then be used to tell is we need the \left ( ... \right ) pair. I've done the test once: you could do it twice and not need to repeat the \frac.

Best Answer

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[Tex/LaTex] the best way to scan over a list of somethings

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