Test if \iffoo is defined before using it

Question

When using tikz in a non-trivial document, the library external is necessary to make PDF build time acceptable (unless one makes a separate TikZ PDF for each figure).

Unfortunately, this library has a number of bugs, such as not working with Beamer overlays. There are fixes, such as this:

\documentclass{beamer}
  \usepackage{tikz}
  \usetikzlibrary{external}
  \tikzexternalize
\makeatletter
\ifdefined\ifbeamer@anotherslide  
\tikzset{
  beamer externalising/.style={%
    execute at end picture={%
      \tikzifexternalizing{%
        \ifbeamer@anotherslide
          \pgfexternalstorecommand{\string\global\string\beamer@anotherslidetrue}%
        \fi
      }{}%
    }%
  }, external/optimize=false, every picture/.style={beamer externalising}
}
\fi
\makeatother
\begin{document}
  \begin{frame}
    \begin{tikzpicture}
      \node {A\qquad\ };
      \pause
      \node {B};
    \end{tikzpicture}
  \end{frame}
\end{document}

The TikZ picture has an overlay, due to the \pause command, and the output is properly generated because of the \tikzset{...} fix.

I would like to put this command in a separate .sty file, together with other general purpose hacks. Of course, if I loaded the style file from a non-Beamer document, \ifbeamer@anotherslide would be undefined. So I need to make the \tikzset{...} command conditional to the Beamer class loading and/or \ifbeamer@anotherslide being defined. I tried several things along these lines:

%%% hack.sty
\ifdefined\ifbeamer@anotherslide  
  \tikzset{
    beamer externalising/.style={%
      execute at end picture={%
        \tikzifexternalizing{%
          \ifbeamer@anotherslide
            \pgfexternalstorecommand{\string\global\string\beamer@anotherslidetrue}%
          \fi
        }{}%
      }}, external/optimize=false, every picture/.style={beamer externalising}
  }
\fi

However, constructs like:

\ifdefined\iffoo
 \iffoo
   % do stuff
 \fi
\fi

are illegal.

How can I have the \tikzset command above to be run only when it is necessary, that is, when there is a Beamer document using overlays, and not when other types of documents are used?

samcarter_is_at_topanswers.xyz · Accepted Answer · 2022-10-15T22:22:21.660

For a general use case, you can use \@ifclassloaded{beamer}{<code for beamer>}{<code for other classes>} to test for the current class.

In case your non-beamer documents happen to use the beamerarticle package, you could also test with modes, e.g. \mode<beamer>{code for beamer class} (see https://tex.stackexchange.com/a/657316/36296 for an example).

Unrelated to the question, but I wouldn't use \pause inside a tikzpicture, this can have all kinds of "funny" side effects, like making footlines disappear. Instead either use the overlay awareness of tikz nodes or have a look at the overlay-beamer-styles tikz library.

% !TeX program = txs:///arara
% arara: pdflatex: {synctex: on, interaction: nonstopmode, shell: yes}
\documentclass{beamer}
  \usepackage{tikz}
  \usetikzlibrary{external}
  \tikzexternalize
\makeatletter
@ifclassloaded{beamer}{
\ifdefined\ifbeamer@anotherslide

\tikzset{
  beamer externalising/.style={%
    execute at end picture={%
      \tikzifexternalizing{%
        \ifbeamer@anotherslide
          \pgfexternalstorecommand{\string\global\string\beamer@anotherslidetrue}%
        \fi
      }{}%
    }%
  }, external/optimize=false, every picture/.style={beamer externalising}
}
\fi
}{}
\makeatother
\begin{document}
  \begin{frame}
    \begin{tikzpicture}
      \node<+-> {A\qquad\ };
      \node<+-> {B};
    \end{tikzpicture}
  \end{frame}
\end{document}

score 3 · Answer 2 · answered Oct 15 '22 at 21:05

Here's a way out for your \iffoo problem: the idea is to never use \iffoo, so TeX will never “see” conditionals.

\documentclass{article}
\ExplSyntaxOn
\NewExpandableDocumentCommand{\BooleanExistsTF}{mmm}
 {
  \cs_if_exist:cTF { if#1 } { #2 } { #3 }
 }
\NewExpandableDocumentCommand{\BooleanExistsT}{mm}
 {
  \cs_if_exist:cT { if#1 } { #2 }
 }
\NewExpandableDocumentCommand{\BooleanTF}{mmm}
 {
  \legacy_if:nTF { #1 } { #2 } { #3 }
 }
\ExplSyntaxOff
\begin{document}
\BooleanExistsTF{foo}{%
  \BooleanTF{foo}{YES}{NO}%
}{DOESN'T EXIST}
\newif\iffoo
\BooleanExistsT{foo}{%
  \BooleanTF{foo}{YES}{NO}%
}
\footrue
\BooleanExistsT{foo}{%
  \BooleanTF{foo}{YES}{NO}%
}
\end{document}

You may want to define also \BooleanExistsF, \BooleanT or \BooleanF.

Test if \iffoo is defined before using it

2 Answers2