\SplitList on several delimiters

Question

How can I tell \SplitList from xparse to split the argument at any one of several delimiters, e.g. either a comma, a semi-colon, etc. The following example works with a list of items separated by commas, but I would like it to work also when the delimiter is a semi-colon.

\documentclass{article}
\usepackage{xparse}
\NewDocumentCommand\foo{>{\SplitList{ , }}m}{{\ProcessList{#1}{\textsf}}}
\begin{document}
 Test \foo{a,b,c} \foo{a;b;c}
\end{document}

Answer 1

You can do it, but it's better to tell explicitly what delimiter you're going to using for the particular list.

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand\foo{O{,}mO{\textsf}}
 {
  \seq_set_split:Nnn \l_lotomat_input_seq { #1 } { #2 }
  \seq_map_function:NN \l_lotomat_input_seq #3
 }
\seq_new:N \l_lotomat_input_seq
\ExplSyntaxOff

\begin{document}

Test \foo{a,b,c} \foo[;]{a;b;c} \foo[:]{a:b:c}[\textbf]

\end{document}

We have to use lower level functions, in order to be able to change the delimiter. I also added the possibility of giving a different one argument function as trailing optional argument.

Here is a different implementation where the delimiter can be either a comma or a semicolon (you can add other substitutions):

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand\foo{mO{\textsf}}
 {
  \tl_set:Nn \l_lotomat_input_tl { #1 }
  \tl_replace_all:Nnn \l_lotomat_input_tl { ; } { , }
  \seq_set_split:NnV \l_lotomat_input_seq { , } \l_lotomat_input_tl
  \seq_map_function:NN \l_lotomat_input_seq #2
 }
\tl_new:N \l_lotomat_input_tl
\seq_new:N \l_lotomat_input_seq
\ExplSyntaxOff

\begin{document}

Test \foo{a,b,c} \foo{a;b;c} \foo{a,b;c}[\textbf]

\end{document}

The output is the same as before.

Answer 2

using \fbox rather than \textsf to make it clearer what has split, you can cascade two list processors (although it's probably bad form to do so).

\documentclass{article}
\usepackage{xparse}
\NewDocumentCommand\foo{>{\SplitList{,}}m}{\ProcessList{#1}\foob}
\NewDocumentCommand\foob{>{\SplitList{;}}m}{{\ProcessList{#1}\fbox}}
\begin{document}
 Test \foo{a,b,c} \foo{a;b;c} \foo{egreg,asked;this}
\end{document}

Answer 3

You can perform a search-and-replace to make sure all your split tokens are the same:

\documentclass{article}

\usepackage{regexpatch}

\NewDocumentCommand\foo{ m }{%
  \def\fooarg{#1}%
  \regexpatchcmd*{\fooarg}{;}{,}{}{}% Replace all ; with ,
  \expandafter\footwo\expandafter{\fooarg}}

\NewDocumentCommand\footwo{>{\SplitList{ , }}m}{{\ProcessList{#1}{\textsf}}}

\begin{document}

Test \foo{a,b,c} \foo{a;b;c}

\end{document}

Answer 4

Here is a listofitems approach, where the possible separators are defined by \setsepchar argument, separated by || "or". Here, , and ; are given.

\documentclass{article}
\usepackage{listofitems}
\newcommand\foo[1]{\setsepchar{,||;}\readlist\foolist{#1}%
  \foreachitem\x\in\foolist{\fbox{\x}}}
\begin{document}
 Test \foo{a,b,c} \foo{a;b;c}

The list length is \foolistlen.  Item 2 is \foolist[2].
\end{document}

The length of the list is available as \foolistlen and the items are accessible as \foolist[1], \foolist[2], etc.

It should furthermore be noted that the original unexpanded tokens can be retrieved by expanding \foolist[] exactly twice:

\documentclass{article}
\usepackage{listofitems}
\usepackage[T1]{fontenc}
\newcommand\foo[1]{\setsepchar{,||;}\readlist\foolist{#1}%
  \foreachitem\x\in\foolist{\fbox{\x}}}
\begin{document}
 Test \foo{a,b,c} \foo{a;\textit{b};c}

The list length is \foolistlen.  Item 2 is \foolist[2], 

stored as \detokenize\expandafter\expandafter\expandafter{\foolist[2]}.
\end{document}