Parse csv-list, function with >1 parameters as callback

Question

In my texts I have to deal with lists, whose items need to be formatted seperatly, i.e.:

\funktion[3][]{T}--\funktion{S}--\funktion[3][7]{D}--\funktion{T}

In \funktion which leads to \emphsubsup the formatting takes place and the optional parameters are handled.

How can I shorten this task by a function like \funktionen? I.e.:

\funktionen{[3][]{T},{Sp},[3][{7,9,11}]{D},{T}} or even better:

\funktionen{[3][]T,Sp,[3][{7,9,11}]D,T}

Each argument can contain more than 1 character, including comma!

I've tried it with forcsvlist from the etoolbox package, but it takes (of course) the whole value [3][]{T} as one single argument. Also I don't know how to realize the seperator --.

MWE:

\documentclass[border=5]{standalone}
\usepackage{etoolbox, xparse, fixltx2e, letltxmacro}

\DeclareDocumentCommand{\subsup}{ o o m }{%
\IfValueTF{#1}{%
    \IfValueTF{#2}{%
    \textsubscript{#1}#3\textsuperscript{#2}%
    }{%
    #3\textsuperscript{#1}}%
}{#3}%
}
\DeclareDocumentCommand{\emphsubsup}{ o o m }{\emph{\subsup[#1][#2]{#3}}}%same, only emphasized

\LetLtxMacro{\funktion}{\emphsubsup}

%test
\newcommand*{\funktionen}[1]{%
    \forcsvlist{\funktion}{#1}
}

\begin{document}

    \funktion[3][]{T}--\funktion{Sp}--\funktion[3][7,9,11]{D}--\funktion{T}

    \hskip1ex

    \funktionen{[3][]{T},{Sp},[3][{7,9,11}]{D},{T}}

\end{document}

Answer 1

As you are really looking for parsing 'beyond' a document command (i.e. this isn't really standard LaTeX2e-style argument to a simple command) I'd be tempted to code the parser bit myself. Assuming you don't need to worry about nested [/] (in which case I guess you do need xparse) we can do it quite simply using a 'classical' look-ahead approach. I've done this in expl3 but it could also be done easily using \@ifnextchar:

\RequirePackage{fixltx2e}
\documentclass{article}
\usepackage{expl3,xparse}
\ExplSyntaxOn
\DeclareDocumentCommand \funktionen { > { \SplitList { , } } m }
  {
    \musicman_parse:n {#1}
  }
\seq_new:N \l__musicman_parse_seq
\tl_new:N \l__musicman_tmp_tl
\cs_new_protected:Npn \musicman_parse:n #1
  {
    \group_begin:
      \seq_clear:N \l__musicman_parse_seq
      \tl_map_inline:nn {#1}
        {
          \tl_clear:N \l__musicman_tmp_tl
          \peek_meaning_ignore_spaces:NTF [ % ]
            { \__musicman_parse_auxi:w }
            { \__musicman_parse_auxiii:w }
          ##1 \q_stop
          \seq_put_right:NV \l__musicman_parse_seq \l__musicman_tmp_tl
        }
      \seq_use:Nn \l__musicman_parse_seq { -- }
    \group_end:
  }
\cs_new_protected:Npn \__musicman_parse_auxi:w [ #1 ]
  {
    \tl_set:Nn \l__musicman_tmp_tl { \textsubscript {#1} }
    \peek_meaning_ignore_spaces:NTF [ % ]
      { \__musicman_parse_auxii:w }
      { \__musicman_parse_auxiii:w }
  }
\cs_new_protected:Npn \__musicman_parse_auxii:w [ #1 ] #2 \q_stop
  {
    \tl_put_right:Nx \l__musicman_tmp_tl
      {
        \exp_not:n {#2}
        \tl_if_blank:nF {#1} { \exp_not:n { \textsuperscript {#1} } }
      }
  }
\cs_new_protected:Npn \__musicman_parse_auxiii:w #1 \q_stop
  { \tl_set:Nn \l__musicman_tmp_tl {#1} }
\ExplSyntaxOff
\begin{document}

\funktionen{[3][]{T},{Sp},[3][{7,9,11}]{D},{T}}

\end{document}

I've used a sequence to hold the 'partial' list of items as this makes it easy to insert the separators (--) without having to do any tests myself for 'end of list' or similar. One could instead use a hand-crafted mapping in this case, but unless performance is vital that tends to be less clear than the approach here.

For the expl3 experts, I note that here we could use \tl_if_head_eq_meaning:nNTF instead of \peek_meaning:NTF as the argument has already been grabbed.

Answer 2

If you don't mind the function being executed inside a TeX group then you could try pgffor:

\documentclass[border=5]{standalone}

\usepackage{etoolbox, xparse, fixltx2e, pgffor}

\DeclareDocumentCommand{\funktion}{ o o m }{%
\IfValueTF{#1}{%
    \IfValueTF{#2}{%
    \textsubscript{#1}#3\textsuperscript{#2}%
    }{%
    #3\textsuperscript{#1}}%
}{#3}%
}

%test
\newcommand*{\funktionen}[1]{%%
  \foreach \args [count=\x]in {#1}{%
    \ifnum\x>1--\fi\expandafter\funktion\args%
  }%
}

\begin{document}

\funktion[3][]{T}--\funktion{S}--\funktion[3][7]{D}--\funktion{T}
\hskip1ex

\funktionen{[3][]{T},{S},[3][7]{D},{T}}

\end{document}

However, a custom list parser is fairly straightforward:

\documentclass[border=5]{standalone}

\usepackage{etoolbox, xparse, fixltx2e}


\DeclareDocumentCommand{\funktion}{ o o m }{%
\IfValueTF{#1}{%
    \IfValueTF{#2}{%
    \textsubscript{#1}#3\textsuperscript{#2}%
    }{%
    #3\textsuperscript{#1}}%
}{#3}%
}

\newcommand*{\Funktionen}[1]{%
  \let\FunctionenNext=\relax%
  \FunctionenLoop#1,\FunctionenHalt,%
}
\def\FunctionenHalt{\FunctionenHalt}%
\def\FunctionenLoop#1,{%
  \def\tmp{#1}%
  \ifx\tmp\FunctionenHalt%
    \let\FunctionenNext=\relax%
  \else%
    \ifx\FunctionenNext\relax\else--\fi%
    \funktion#1%
    \let\FunctionenNext=\FunctionenLoop%
  \fi%
  \FunctionenNext%
}
\begin{document}

\funktion[3][]{T}--\funktion{S}--\funktion[3][7]{D}--\funktion{T}

\hskip1ex

\Funktionen{[3][]{T},{S},[3][7]{D},{T}}

\end{document}

The result is the same as before.

Answer 3

The solution without need to any LaTeX package follows. After

\funktionen{[3][]T,Sp,[3][7,9,11]D,T}

you have stored the following content:

\funktion[3][]{T}--\funktion{Sp}--\funktion[3][7,9,11]{D}--\funktion{T}

in \funktionenL macro. You can execute it by simply running \funktionenL.

\long\def\addto#1#2{\expandafter\def\expandafter#1\expandafter{#1#2}}

\def\funktionen#1{\def\funktionenL{}\funktionenA#1,,}
\def\funktionenA{\let\tmpa=\relax \let\tmpb=\relax \futurelet\next\funktionenB}
\def\funktionenB{\ifx\next[\expandafter\funktionenC \else \expandafter\funktionenF \fi}
\def\funktionenC[#1]{\def\tmpa{#1}\futurelet\next\funktionenD}
\def\funktionenD{\ifx\next[\expandafter\funktionenE \else \expandafter\funktionenF \fi}
\def\funktionenE[#1]{\def\tmpb{#1}\funktionenF}
\def\funktionenF#1,{\ifx,#1,\else
   \ifx\funktionenL\empty \else \addto\funktionenL{--}\fi
   \addto\funktionenL{\funktion}%
   \ifx\tmpa\relax\else \funktionenG{\expandafter[\tmpa]}\fi
   \ifx\tmpb\relax\else \funktionenG{\expandafter[\tmpb]}\fi
   \addto\funktionenL{{#1}}%
   \expandafter\funktionenA
   \fi
}
\def\funktionenG{\expandafter\addto\expandafter\funktionenL\expandafter}

\funktionen{[3][]T,Sp,[3][7,9,11]D,T}

\message{\meaning\funktionenL}