Parsing optional macro arguments

Question

I am trying to define a macro with flexible arguments: 3 mandatory and 2 optional ones - like this:

\macro{<enter code here>}[arg2] arg3 = arg4 | arg5;

So args 2 and 5 are optional, as is the |.

I got quiet close to solving this with ideas found here and here.

Now I am stuck somewhere in TeX's stomach. Maybe someone can shed some light on the problem - I am a total newbie and I think, there must be plenty of possibilities. I have tried a lot but am not familiar enough with \expandafter, \futurelet, \xdef & friends. I am stuck here:

\makeatother
\def\@pop#1{}
\def\@split#1;{\def\@@tmp{#1|}\expandafter\@@split\@@tmp\@end@token}
\def\@@split#1|{\@ifnextchar\@end@token{{#1}{}\@pop}{\@@@split{#1}}}
\def\@@@split#1#2|{{#1}{#2}\@pop}

\def\display#1{\@ifnextchar[{\@display{#1}}{\@display{#1}[1]}}
\def\@display#1[#2]#3={\def\@tmp{\@@display{#1}{#2}{#3}}\expandafter\@tmp\@split}

\def\@@display#1#2#3#4#5{*#1*#2*#3*#4*#5*}
\makeatletter

\display{aaa}[bbb] AAA = BBB | CCC;

the output is supposed to look like this:

*aaa*bbb*AAA*BBB*CCC*

but instead I get

/tmp/problem.tex:56: Missing control sequence inserted.
<inserted text>
                \inaccessible 
l.42 \display{aaa} AAA = BBB;

...am using a href="http://gummi.midnightcoding.org/"gummi/a ...good stuff IMHO!

Answer 1

A solution using LaTeX2e just for \@ifnextchar:

\documentclass{article}
\makeatletter
\def\display#1{%
  \@ifnextchar[%]
    {\display@aux@i{#1}}
    {\display@aux@i{#1}[]}%
}
\def\display@aux@i#1[#2]#3=#4;{%
  \display@aux@ii{#1}{#2}{#3}#4||\@nil
}
\def\display@aux@ii#1#2#3#4|#5|#6\@nil{%
  *#1*#2*#3*#4*#5*
}
\makeatother
\begin{document}
\noindent
\display{aaa}[bbb] AAA = BBB | CCC; \\
\display{aaa}[bbb] AAA = BBB ;
\end{document}

Alternative xparse-based solution:

\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\DeclareDocumentCommand \display 
  { m o u { = } > { \SplitArgument { 1 } { | } } u { ; } } {
  * #1 * #2 * #3 * \display_aux:nn #4 *  
}
\cs_new:Npn \display_aux:nn #1#2 { #1 * #2 }
\ExplSyntaxOff
\begin{document}
\noindent
\display{aaa}[bbb] AAA = BBB | CCC; \\
\display{aaa}[bbb] AAA = BBB ;
\end{document}

Answer 2

the same, only the other way round :-)

\documentclass{minimal}

\makeatletter
\def\display#1{\@ifnextchar[{\display@i{#1}}{\display@i{#1}[]}}
\def\display@i#1[#2]#3;{\display@ii#3||\@nil{#1}[#2]}
\def\display@ii#1=#2|#3|#4\@nil#5[#6]{*#5*#6*#1*#2*#3*}

\def\blub{\@ifnextchar[\blub@i{\blub@i[]}}
\def\blub@i[#1]#2;{\blub@ii[#1]#2++\@nil}
\def\blub@ii[#1]#2+#3+#4\@nil{blub[#1] & #2 & #3}
\makeatother


\makeatother

\begin{document}

\display{aaa}[bbb] AAA = BBB|CCC;

\display{aaa}[bbb] AAA = BBB;

\end{document}

Answer 3

You have already received valid LaTeX solution, but for someone else who wants to do something similar in ConTeXt, I am including a ConTeXt solution. This is essential similar to LaTeX solutions using \@ifnextchar, but use a higher level macro \dodoubleargument that checks for two optional arguments (ConTeXt also provides other variants of \do...argument: single, double, triple, quadruple, quintuple, sixtuple, and seventuple).

\def\Macro#1%
  {\dodoubleargument\doMacro[#1]}

\def\doMacro[#1][#2]#3=#4;%
  {\dostartMacro{#1}{#2}{#3}#4||\dostopMacro}

\def\dostartMacro#1#2#3#4|#5|#6\dostopMacro
  {*#1*#2*#3*#4*#5*}

\starttext
\startlines
\Macro{aaa} AAA = BBB ;
\Macro{aaa} AAA = BBB | CCC ;
\Macro{aaa}[bbb] AAA = BBB ;
\Macro{aaa}[bbb] AAA = BBB | CCC; 
\stoplines
\stoptext

Answer 4

Here's yet another LaTeX solution not unlike this related answer of mine; the new feature is that it's completely free of explicit calls of \@ifnextchar. (This also makes \makeatletter / \makeatother dispensable, so maybe it's a bit more accessible for the end user.)

\documentclass{minimal}
\newcommand\display[1]{*#1*\displayi}
\newcommand\displayi[1][]{#1*\displayii}
\def\displayii#1=#2;{#1*\displayiii#2||;}
\def\displayiii#1|#2|#3;{#1*#2}
\begin{document}
\display{aaa} AAA = BBB | CCC; \par
\display{aaa}[bbb] AAA = BBB | CCC; \par
\display{aaa}[bbb] AAA = BBB ;
\end{document}

Note that I used the fact that the arguments #1 to #5 occur in their natural order in the replacement of \display; this could be adjusted if needed.

Answer 5

I learned a lot - now let me show off this pure TeX version, using \futurelet: (if you can shorten it, feel free to edit)

\documentclass{article}

\def\b{\ba[]}
\def\ba[#1]#2;{\bar{#1}#2++\nil}
\def\bar#1#2+#3+#4\nil{blub[#1]&#2&#3}
\def\blu{\ifx\next[\let\f\ba\else\let\f\b\fi\f}
\def\blub{\futurelet\next\blu}

\begin{document}
\begin{tabular}{lll}
\blub foo;                  \\
\blub[bla] bar;                     \\
\blub foo + bar;            \\
\blub[bla] foo + bar;               \\
\end{tabular}
\end{document}

Oh ... i was just wondering how remote images can NOT be disabled ...