how to redefine environments like \begin{xxx} ... \end{xxx}

Question

I'm translating some text that use the comment package, it's usage seems like that:

\begin{en}
 ... some English text
\end{en}

\begin{zh}
... corresponding Chinese text
\end{zh}

By using \excludecommand{en} or \includecommand{en} before \begin{document}, we can control the text out or in the final PDF document.

But this too trouble to add \begin{}/\end{} for every paragraph, what I want is following:

\en{
 ... some English text
}

\zh{
... corresponding Chinese text
}

this is much more simple to type. and I create the commands like this:

\newcommand{\zh}[1]{\begin{zh}#1\end{zh}}
\newcommand{\en}[1]{\begin{en}#1\end{en}}

But this cause compile error like runaway argument, how to make it work under this situation by using newcommand?

Answer 1

The problem is that you are trying to redefine an existing command \en which gets defined when the en environment is defined (as does \enden). The solution to redefine most environments is to first save the definition of xxx as \OldXxx:

\let\OldXxx\xxx

and then redefine the \xxx macro using \OldXxx and \endxxx:

\renewcommand{\xxx}[1]{\OldXxx#1\endxxx}

Note:

• As per the comments, this won't work with any verbatim type of environments.

Code:

\documentclass{article}
\newenvironment{en}{%
}{%
}%
\begin{document}
\begin{en}
 \ldots some English text in environment
\end{en}
\let\OldEn\en
\renewcommand{\en}[1]{\OldEn#1\enden}
\en{\ldots some more English text in macro \ldots}
\end{document}

Answer 2

Use just one other character for the command:

\documentclass{article}
\newenvironment{en}{}{}
\newenvironment{zh}{}{}

\newcommand\Zh[1]{\begin{zh}#1\end{zh}}
\newcommand\En[1]{\begin{en}#1\end{en}}

%\renewcommand\Zh[1]{} %%% enable if it should be excluded
%\renewcommand\En[1]{} %%% enable if it should be excluded

\begin{document}
\En{ \ldots some English text in environment (En)}

\Zh{ \ldots some more English text in macro \ldots (Zh)}

\end{document}