[Tex/LaTex] How to write a macro having comma-separated and variable number of arguments

comma-separated listmacrosparsing

I want to write a macro in LaTeX2e that can pass \textcolor, which is embedded in another macro, the values of the colour model gray, rgb, or cmyk. The number of arguments specified implies the colour model to be used; 1 argument for gray, 3 for the rgb, and 4 for the cmyk model. I was able to write a macro that does what I want, but with the arguments in the standard manner in braces. This is the code I was able to write by modifying the answers here.

\makeatletter  
\def\setmycolour#1{%  
\@ifnextchar\bgroup%  
    {\docolour{#1}}  
    {\dogray{#1}}  
}  
\def\dogray#1{This is gray hue #1.}  
\def\docolour#1#2#3{%  
\@ifnextchar\bgroup%  
    {\docmyk{#1}{#2}{#3}}  
    {\dorgb{#1}{#2}{#3}}  
}  
\def\dorgb#1#2#3{This is rgb colour #1,#2,#3.}  
\def\docmyk#1#2#3#4{This is cmyk colour #1,#2,#3,#4.}  
\makeatother

I use the macro as

\setmycolour{0.85}\\
\setmycolour{1}{0}{0}\\
\setmycolour{1}{0}{0}{0}\

I want to use the macro, for example, as \setmycolour{1,0,0} or \setmycolour{0.85}. How do I parse the arguments in the macro definition to do this? Is the above code the best way to get the effect I want?

Best Answer

The comments what color we have is only for demonstration here.

\documentclass{article}
\usepackage[T1]{fontenc}

\makeatletter  
\def\setmycolour#1{\expandafter\setmycolour@i#1,,,,\@nil}
\def\setmycolour@i#1,#2,#3,#4,#5\@nil{% 
  \ifx$#2$ we have gray => #1 \else
    \ifx$#3$ we have a wrong color setting \else
      \ifx $#4$ we have a rgb setting => #1,#2,#3\else
                we have a cmyk setting =>#1,#2,#3,#4
      \fi
    \fi
  \fi 
}  
\makeatother

\begin{document}

\setmycolour{0.5}\par
\setmycolour{0.5,0.6}\par
\setmycolour{0.5,0.6,0.7}\par
\setmycolour{0.5,0.6,0.7,0.8}\par

\end{document}

Related Solutions

[Tex/LaTex] \newcommand and comma separated parameters

I think you should ask what you want in full generality. For your concrete example,

\newcommand*\swap[1]{\doswap#1\relax}
\def\doswap#1,#2\relax{{#2,#1}}

should work, although I didn't test it.

[Tex/LaTex] parse variable length comma separated list into command

Here's an option using sequences, it could probably be made a little more compact as the code from the two helper macros is almost identical.

I'm not an expert so take my advice with a grain of salt but I would just stick with using sequences. They require an extra line of code here and there, but the additional options that they provide are well worth it.

\documentclass{article}
\usepackage{xparse}
\usepackage{siunitx}
\ExplSyntaxOn
\NewDocumentCommand{\sumofsquares}{ m o }
    {
        \IfNoValueTF {#2}
            % if optional is missing call this
            {\sum_of_squares:n {#1}}
            % if not, then call this
            {\sum_of_squares:nn {#1}{#2}}
    }

\cs_new_protected:Npn \sum_of_squares:n #1
    {
        % does what the name suggests, set a sequence from the clist
        \seq_set_from_clist:Nn \l_tmpa_seq {#1}
        % applies final arg to each element of second seq and stores result in first seq
        \seq_set_map:NNn \l_tmpb_seq \l_tmpa_seq {(##1)^2}
        % \seq_use puts the items from the seq back in the input with "+" as a separator
        \sqrt{\seq_use:Nnnn \l_tmpb_seq {+}{+}{+}}
    }
\cs_new_protected:Npn \sum_of_squares:nn #1 #2
    {
        % same as above, but with the addition of units
        \seq_set_from_clist:Nn \l_tmpa_seq {#1}
        \seq_set_map:NNn \l_tmpb_seq \l_tmpa_seq {(\SI{##1}{#2})^2}
        \sqrt{\seq_use:Nnnn \l_tmpb_seq {+}{+}{+}}
    }


\ExplSyntaxOff
\begin{document}

$\sumofsquares{2,3,-4}$\par\medskip
$\sumofsquares{2,3,-4}[m/s]$

\end{document}

Here's a slightly shorter (and less clear) example using clists. The same method could have been used to shorten the code above.

\documentclass{article}
\usepackage{xparse}
\usepackage{siunitx}
\ExplSyntaxOn

\NewDocumentCommand{\sumofsquares}{ m O{} }
    {
        \sum_of_squares:nn {#1}{#2}
    }

\cs_new_protected:Npn \sum_of_squares:nn #1 #2
    {
        \tl_if_empty:nTF {#2}
            {
                \clist_set:Nn \l_tmpa_clist {#1}
                \sqrt{(\clist_use:Nnnn \l_tmpa_clist {)^2+(} {)^2+(} {)^2+(} )^2 }
            }
            {
                \clist_set:Nn \l_tmpa_clist {#1}
                \sqrt{(\clist_use:Nnnn \l_tmpa_clist {\,\si{#2})^2+(} {\,\si{#2})^2+(} {\,\si{#2})^2+(} \,\si{#2})^2}
            }
    }

\ExplSyntaxOff
\begin{document}

$\sumofsquares{2,3,-4}$\par\medskip
$\sumofsquares{2,3,-4}[m/s]$

\end{document}

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