code fails to be wrapped with condition

Question

In the following example, I want the content in minipage is highlighted by \colorbox if the condition is true. If the condition is false, the content in minipage typeset directly.

The typeset of true-branch however, is not highlighted. I think it is because of \fi.

Then,how to modify this code to make it work as expected?

Code:

\documentclass{article}
\usepackage{xcolor}
\begin{document}
\ifnum 5>1 % or something like \ifx..., \if\empty..., and so on.
\colorbox{red} \fi
{\begin{minipage}{2in}The content maybe very large and complex, I don't want to duplicate it in both true-branch and false-branch\end{minipage}}
\end{document}

Similar: https://tex.stackexchange.com/a/35810 – muzimuzhi Z Jul 09 '22 at 01:59 — muzimuzhi Z, Jul 09 '22 at 01:59

score 1 · Accepted Answer · answered Jul 09 '22 at 01:59

1

\documentclass{article}
\usepackage{xcolor}

\makeatletter
\newcommand\myConditionTF[1]{%
  #1% or something like \ifx..., \if\empty..., and so on.
    \expandafter\@firstoftwo
  \else
    \expandafter\@secondoftwo
  \fi
}
\makeatother

\begin{document}

\myConditionTF{\ifnum 5>1\relax}
  {\colorbox{red}}
  {}
{\begin{minipage}{2in}The content maybe very large and complex, I don't want to duplicate it in both true-branch and false-branch\end{minipage}}
\qquad
\myConditionTF{\ifnum 5<1\relax}
  {\colorbox{red}}
  {}
{\begin{minipage}{2in}The content maybe very large and complex, I don't want to duplicate it in both true-branch and false-branch\end{minipage}}
\end{document}

answered Jul 09 '22 at 01:59

muzimuzhi Z

26,474

Many thanks for this solution!! And why is \enxpandafter needed? Where or what is the details about \@firstoftwo and @secondoftwo? – lyl Jul 09 '22 at 02:33
1

@lyl To expand hence get rid of the \else and/or \fi. You can get more info about \@firstoftwo and \secondoftwo by searching for them on this site, the internet, or texdoc macros2e, and even by executing latexdef -s \@firstoftwo in terminal. – muzimuzhi Z Jul 09 '22 at 02:38
1

Also see What do \@firstoftwo and \@secondoftwo do? – muzimuzhi Z Jul 09 '22 at 02:39
The first test typesets the content with background color red as expected. When I remove \relax from its argument, the red color disappears. Since #1 is wrapped by braces when calling this macro, why is \relax obligatory here? – lyl Jul 10 '22 at 08:50
@lyl Similar: Use of \relax after \ifnum ... \fi construction – muzimuzhi Z Jul 10 '22 at 11:25

code fails to be wrapped with condition

1 Answers1