comment-package and macro definitions

Question

I want to use the comment package to selectively include/exclude parts of a document. While "\begin{sol}" and "\end{sol}" pairs, combined with \includecomment or \excludecomment would work for selectively including solutions to homework problems, I'd rather write \version{sol} and \endversion{sol}. Knowing that making macros whose names start with "end" is tricky, I went with \eversion. This did not work: apparently a macro that puts \end{sol} into a document is different from \end{sol} in some way I don't understand:

\documentclass{article}
\RequirePackage{comment}

\excludecomment{sol}

\newcommand{\version}[1]%
  {\begin{#1}}

\newcommand{\eversion}[1]%
  {\end{#1}}

\begin{document}
Test.
\version{sol}
Test text.
\eversion{sol}
%\end{sol}
\end{document}

This generates an error with pdflatex ("File ended while scanning use of \next") , but if I comment out the "eversion" line and uncomment \end{sol}, it works. Can someone explain why?

Answer 1

As suggested in the comments, I recommend using something like \begin{version}...\end{version} together with \excludecomment{version}.

If this is not possible then I suggest writing your own "comment-like" environment by hand. To me using \version{sol}...\endversion{sol} seems way too cumbersome (because the sol is a dummy argument that is not actually doing anything), so I would use \version{...}.

Here is one way to do this:

\documentclass{article}
\newif\ifSolutions% define \ifSolutions <solutions code>\else <no solutions code>\fi.

\newcommand\version[1]{\ifSolutions #1\fi}% print #1 only if \Solutionstrue

\begin{document}
  Test

  \Solutionsfalse\version{Solutions are off}% should not print

  \Solutionstrue\version{Solutions are on}% should print

\end{document}

This produces:

If you really want to use \version{sol}...\endversion{sol} then here is a horrible hack that will let you do this:

\documentclass{article}
\newif\ifSolutions% define \ifSolutions <solutions code>\else <no solutions code>\fi.

\long\def\version#1#2\endversion#3{\ifSolutions #2\fi}

\begin{document}
  Test

  \Solutionsfalse\version{sol}Solutions are off\endversion{sol}

  \Solutionstrue\version{sol}Solutions are on\endversion{sol}

\end{document}

This gives you the syntax that you wanted but I do not recommend that you use this! What the code is doing is defining \version to be a macro that expects three arguments with \endversion between the second and third arguments. The second argument is printed if \Solutionstrue and the first and third arguments are discarded. The \long is needed because this allows #2, the real argument, to contain paragraph breaks, which you will probably want in your use-case. This macro is an abuse of the TeX language and it will probably earn me some down-votes for even suggesting this!

If you want to go this route then I recommend dropping the {sol}'s and using:

\long\def\version#1\endversion{\ifSolutions #1\fi}

\version Sol/version code\endversion