Hiding part of the text when certain macro is enabled

Question

Problem

I am now preparing exercises for the course I am going to teach next quarter. I have two concerns

• Writing problem descriptions and corresponding solutions in two separated files are pretty annoying since it may require lots of copy and paste in later days.
• Using hyperlinks to jump between problem description and solution is also annoying since some problem descriptions are rather long and involving a lot of fine details, which would make both my life and students' life harder.

I am wondering if there is a mechanism that could hide selected part of the text from global setting. I know I could use comment but

• It seems that I need to comment all individual spots. I do not know how to comment all the parts I need to comment (there are more than 200 exercises I am planning to write).

Answer 1

Here is one way using etoolbox and environ:

\documentclass{article}
\usepackage{environ}
\usepackage{etoolbox}

\newtoggle{doPrintStuff}        % the toggle is initially false

% Uncomment this if you don't want spaces after \end{maybePrint} to be
% discarded (the default is \environfinalcode{\ignorespacesafterend}, which
% causes such spaces to be ignored):
%
%\environfinalcode{}

\NewEnviron{maybePrint}{%
  \iftoggle{doPrintStuff}{\BODY}{}%
}

\begin{document}
X%
\begin{maybePrint}
  $\langle$environment contents$\rangle$
\end{maybePrint}
Y

\toggletrue{doPrintStuff}

X%
\begin{maybePrint}
  $\langle$environment contents$\rangle$
\end{maybePrint}
Y

X%
\begin{maybePrint}%
  $\langle$environment contents$\rangle$%
\end{maybePrint}
Y
\end{document}

Answer 2

You can define your macro, e.g., \comment that hides its content when some if-switch is activated. The following code introduces such a macro and the visibility of the \comment-content can be handled by enabling/disabling the \commenttrue part.

\documentclass{article}

\newif\ifcomment


\def\comment#1{%
    \ifcomment\relax\else #1\fi}

% \commenttrue


\begin{document}
%------------------------
Problem statement\dots

\comment{Solution of the problem: \dots}
%------------------------
\end{document}