Save the body of an environment to a macro, without typesetting

Question

I am trying to save the contents (i.e., the body) of an environment into a macro for later use (in order to typeset it later in the document). I thought of using the environ package (see the minimal example below), but I get an error if there are other macros inside the body of the environment (like a \textbf{bold text}).

\documentclass{article}
\usepackage{environ}
\newcounter{problemnumber}\setcounter{problemnumber}{0}
\NewEnviron{problem}{%
    \stepcounter{problemnumber}
    \expandafter\long\expandafter\xdef\csname myproblem-\theproblemnumber\endcsname{\BODY}
    }
\begin{document}
\begin{problem}
Some equation: $E=mc^2$
\end{problem}
\begin{problem}
Some text.
A second paragraph with a \textbf{bold text}. And an inline equation: $E=mc^2$.
\end{problem}
...
Typsetting the problems in a different order, later in the document.
\textbf{Problem 2:}\quad\csname myproblem-2\endcsname\par\hrulefill
\textbf{Problem 1:}\quad\csname myproblem-1\endcsname\par\hrulefill
\end{document}

you have what you want in \BODY the error is unrelated, you can not have \textbf (or most latex) in \xdef. — David Carlisle, Jan 14 '21 at 20:14
Apart from this approach (environ package) there's also VerbatimOut from fancyvrb, or scontents (see https://tex.stackexchange.com/a/513810/250119 ) — user202729, Nov 01 '21 at 14:25

score 9 · Accepted Answer · answered Jan 14 '21 at 20:17

It is never safe to place arbitrary LaTeX content in edef or xdef.

The macro you want is already defined as \BODY so you need \let not \xdef to give it a global name,

\documentclass{article}
\usepackage{environ}
\newcounter{problemnumber}\setcounter{problemnumber}{0}
\NewEnviron{problem}{%
    \stepcounter{problemnumber}%%%%%%
    \global\expandafter\let\csname myproblem-\theproblemnumber\endcsname\BODY
    }
\begin{document}
\begin{problem}
Some equation: $E=mc^2$
\end{problem}
\begin{problem}
Some text.
A second paragraph with a \textbf{bold text}. And an inline equation: $E=mc^2$.
\end{problem}
...
Typsetting the problems in a different order, later in the document.
\textbf{Problem 2:}\quad\csname myproblem-2\endcsname\par\hrulefill
\textbf{Problem 1:}\quad\csname myproblem-1\endcsname\par\hrulefill
\end{document}

score 9 · Answer 2 · answered Jan 14 '21 at 20:26

You should use \global\let as pointed out by David.

Here's a shorter implementation with also an interface to print the problems.

\documentclass{article}
\ExplSyntaxOn
\seq_new:N \g_digitalink_problem_seq
\NewDocumentEnvironment{problem}{+b}
 {
  \seq_gput_right:Nn \g_digitalink_problem_seq { #1 }
 }
 {}
\NewExpandableDocumentCommand{\getproblem}{m}
 {
  \seq_item:Nn \g_digitalink_problem_seq { #1 }
 }
\ExplSyntaxOff
\begin{document}
\begin{problem}
Some equation: $E=mc^2$
\end{problem}
\begin{problem}
Some text.
A second paragraph with a \textbf{bold text}. And an inline equation: $E=mc^2$.
\end{problem}
Typesetting the problems in a different order, later in the document.
\bigskip
\textbf{Problem 2:}\quad\getproblem{2}\par\hrulefill
\textbf{Problem 1:}\quad\getproblem{1}\par\hrulefill
\end{document}

Save the body of an environment to a macro, without typesetting

2 Answers2