[Tex/LaTex] How to pass an optional argument to an environment with verbatim content

environmentsoptional argumentsverbatim

This is an attempt to make clear what happened in this question of xport (now deleted, sorry). The now deleted question included code that tried to make my answer to this question of xport work for optional arguments, but the code failed. A shorter illustration: The following code doesn't compile if one removes the [optional argument].

\documentclass{minimal}
\usepackage{listings,fancyvrb}

\newenvironment{Row}[1][]
    {\VerbatimEnvironment
     \begin{VerbatimOut}{\jobname.tmp}}
    {\end{VerbatimOut}\lstinputlisting{\jobname.tmp}}

\begin{document}
\begin{Row}[optional argument]
\relax
\end{Row}
\end{document}

The error message says

! FancyVerb Error:
  Extraneous input `\relax ' between \begin{Row}[<key=value>] and line end

Of course, the optional argument (and in fact the whole construction) is utterly pointless here, but hey, it's a minimal example. To make the example in xport's question also work for optional arguments is quite interesting, I think.

The question: What exactly is happening here, and how can one fix the code?

(What I found out so far: \begin{VerbatimOut}{\jobname.tmp}} wants to see a linebreak immediately after it (try putting a %), and this somehow gets messed up by \begin{Row} looking for the optional argument.)

Best Answer

EDIT: TH.'s answer is much simpler. The one below should depend less on the details of the implementation of \VerbatimEnvironment, but that's the only good thing about it.

I propose the following code. The idea is to make a new environment (which I called Row, renaming the old Row to oldRow) check for an optional argument "by hand", and write the relevant thing to a file. Then the file (\jobname.row) is read so that fancyvrb can happily set the relevant catcodes.

All this can probably be done using \scantokens, but I am still quite confused about newlines inside \scantokens.

I also added *#1* to your definition of the environment: this way, we can check what is going on with the optional argument.

\documentclass{minimal}
\usepackage{listings,fancyvrb}

\newenvironment{oldRow}[1][]
{*#1*\VerbatimEnvironment
  \begin{VerbatimOut}{\jobname.tmp}}
  {\end{VerbatimOut}\lstinputlisting{\jobname.tmp}}


\begin{document}

% ==============================================
\makeatletter
\newwrite\RowWrite

\newcommand{\makeallother}{%
  \count0=0\relax 
  \loop\relax 
  \catcode\count0=12\relax 
  \advance\count0 by 1\relax 
  \ifnum\count0<256\relax
  \repeat\relax}

\newenvironment{Row}{%
  \makeallother
  \futurelet\next
  \Row@aux@i}{}

\newcommand{\Row@aux@i}{%
  \def\Row@optional@arg{}%
  \ifx[\next
  \expandafter\Row@grab@until@bracket
  \else
  \expandafter\Row@grab@until@end
  \fi}

\def\Row@grab@until@bracket[#1]{%
  \def\Row@optional@arg{#1}\Row@grab@until@end}

% First expand the \csname...\endcsname,
% then the \string, then the \def.
\expandafter\expandafter\expandafter\def
\expandafter\expandafter\expandafter\Row@grab@until@end
\expandafter\expandafter\expandafter#%
\expandafter\expandafter\expandafter1%
\expandafter\string\csname end{Row}\endcsname{%
  \begingroup%
  \newlinechar=`\^^M%
  \immediate\openout\RowWrite\jobname.row\relax%
  \immediate\write\RowWrite{%
    \string\begin{oldRow}[\Row@optional@arg]#1\string\end{oldRow}%
  }%
  \immediate\closeout\RowWrite%
  \endgroup%
  \end{Row}\input{\jobname.row}%
}

\makeatother
% ==============================================

\begin{Row}
  \relax
  \relax
\end{Row}

\begin{Row}[option]
  \relax
  \relax
\end{Row}


\end{document}
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