Split the \@authors list at \and

Question

With xparse it's pretty easy to split a list at each occurrence of a token. In my MWE I set up a new command \mylist in which I passes two names separated by \and. The xparse script splits the list at the \and token and outputs the two names under each other.

Is there a possibility to use this script with the \@author macro. I'd like to print the authors passed to \author{} one after the other in the \maketitle command. To make sure that LaTeX can normally use the author-command where I used to, I don't want to use the example code (underneath the MWE).

---

MWE

\documentclass{article}
\usepackage{xparse}
\NewDocumentCommand\mylist{>{\SplitList{\and}}m}
    {
    \ProcessList{#1}{\insertitem}
    }
\newcommand\insertitem[1]{#1\\}

\begin{document}

\noindent \emph{Authors:}\\
\mylist{John Doe \and Jane Doe}

\end{document}

---

Author Example

...
\RenewDocumentCommand\author{>{\SplitList{\and}}m}
...
\author{John Doe \and Jane Doe}
...

---

Count

I have set up a counter and add 1 for every item, so at the end I know how many authors were passed to the list. I then check with a conditional if the value of the counter is greater than 1. With this I could decide if Author or Authors should be output before the names. This does not work at the moment because I need the result before the array is defined. If I could use the default LaTeX \author command, this problem would not occur, because the \author command is populated in the preamble. Then the \maketitle shoulr prints out the authors as shown in the MWE.

\documentclass{article}
\usepackage{xparse}
\RenewDocumentCommand\author{>{\SplitList{\and}}m}
    {
    \ProcessList{#1}{\insertitem}
    }

\newcounter{numberOfAuthors}

\newcommand\insertitem[1]{%
    #1%
    \newline%
    \addtocounter{numberOfAuthors}{1}
}

\makeatletter
\newcommand\checkIfGreatherThan{%
    \ifnum\c@numberOfAuthors>1
        \noindent There are \thenumberOfAuthors\ authors given. The output should be \emph{Authors:}
    \else 
        \noindent There is only one author given. The output should be \emph{Author:}
  \fi}
\makeatother

\begin{document}

\noindent \emph{Authors:}\\
% uncomment one of the two commands to test
% \author{John Doe \and Jane Doe}
% \author{John Doe}

\checkIfGreatherThan

\end{document}

Answer 1

Since both \author and \@author are macros that are 'volatile', i.e. \let to \relax after usage of \maketitle, it is better to store the content of the argument of \author to another macro, which is evaluated later on.

The \and macro is 'complicated' in the sense that it is actually closing a tabular environment and starting another one. I decided to redefine \and to expand to , and use the expl3 macro \seq_set_from_clist:Nx in order to split the list into the individual names.

\documentclass{article}
\usepackage{xparse}



\ExplSyntaxOn

\cs_generate_variant:Nn \seq_set_from_clist:Nn {No,Nx}

\NewDocumentCommand{\myinternalsplitter}{m}{%
  \group_begin:
  \seq_set_from_clist:Nx \l_tmpa_seq {#1}% Split the expanded list, i.e. `\and` will place `,` 
  \int_compare:nNnTF { \seq_count:N \l_tmpa_seq } = {1} {% Count the number of items
    \displayauthorhead
  }{
    \displayauthorshead
  }
  \seq_map_inline:Nn \l_tmpa_seq {\insertitem{##1}}% Display the list with `\insertitem
  \group_end:
}

\ExplSyntaxOff


\makeatletter

\let\latex@@author\author

\RenewDocumentCommand{\author}{m}{%
  \latex@@author{#1}% Use the old command
  \gdef\@@authorlist{#1}%
}

\NewDocumentCommand{\displayauthorhead}{}{%
  Author: 

}

\NewDocumentCommand{\displayauthorshead}{}{%
  Authors:

}


\NewDocumentCommand\mylist{}{%
  \begingroup
  \def\and{,}
  \edef\@authorlist{\@@authorlist}
  \myinternalsplitter{\@authorlist}
  \endgroup
}
\makeatother

\newcommand\insertitem[1]{%
  #1

}


\author{John Doe \and Jane Doe \and John Hannibal Smith \and B.A. Baracus}

\begin{document}
\title{Foo}

\mylist%


\maketitle


\end{document}

Answer 2

As you linked this question in another one of yours with a similar scope you could use the same technique that I employed there to solve it (delimited arguments) as an alternative to xparse:

\documentclass{article}
\usepackage{xpatch}

\makeatletter
\newcounter{authors}
\stepcounter{authors}
\def\@author{\textit{Author\ifnum\theauthors>1s\fi:}\\}
\def\split@and#1\and#2{%
  \g@addto@macro\@author{#1\\}%
  \ifx#2\@nil\else
    \stepcounter{authors}%
    \expandafter\split@and\expandafter#2\fi
}
\def\author#1{\split@and#1\and\@nil}
\makeatother

\title{title}
\author{John Doe}%\and Jane Doe}

\begin{document}
\maketitle
\end{document}