Define Command/Macro with boolean flag

Question

I'd love to have a command with a boolean flag. That flag is supposed to be used in a conditional statement.

I'd love to have something like this:

\command             -> false
\command[flag=false] -> false

\command[flag]       -> true
\command[flag=true]  -> true

In the definition I'd have a switch like this:

\iftrue{#flag} true \else false \fi

Have a look at the key value packages we recommended yesterday, e.g. pgfkeys. See https://tex.stackexchange.com/questions/34312/how-to-create-a-command-with-key-values — TeXnician, Aug 01 '18 at 14:11
that for example is exactly how clip works in \includegraphics (defined using the keyval package) — David Carlisle, Aug 01 '18 at 14:11
Well, I see how I could create a value, but not how I could handle the \command[flag] case... — BrainStone, Aug 01 '18 at 14:19
What's wrong with \newif\ifflag, \flagtrue, \flagfalse, \ifflag..\else..\fi? — Ulrich Diez, Aug 02 '18 at 16:51
@UlrichDiez nothing other that I know nothing about conditionals in LaTeX — BrainStone, Aug 02 '18 at 19:55
@BrainStone \newif\ifflag creates a new \if...-conditional. Calling \flagtrue causes \ifflag..\else..\fi to henceforth go the \if..-branch. Calling \flagfalse causes \ifflag..\else..\fi to henceforth go the \else..-branch. — Ulrich Diez, Aug 03 '18 at 19:06

score 4 · Accepted Answer · answered Aug 01 '18 at 14:27

Use an advanced key-value interface, here is expl3:

\documentclass{article}

\usepackage{xparse}

\ExplSyntaxOn

\NewDocumentCommand{\command}{O{}}
 {
  \keys_set:nn { brainstone/command }
   {
    flag=false, % initialize to false
    #1
   }
  %
  \bool_if:NTF \l_brainstone_command_flag_bool
   {
    The ~ flag ~ is ~ set ~ to ~ true
   }
   {
    The ~ flag ~ is ~ set ~ to ~ false
   }
 }

\keys_define:nn { brainstone/command }
 {
  flag .bool_set:N = \l_brainstone_command_flag_bool,
  flag .default:n  = true,
 }

\ExplSyntaxOff

\begin{document}

\command           \ $\to$ false

\command[flag=false] $\to$ false

\command[flag]       $\to$ true

\command[flag=true]  $\to$ true

\end{document}

The flag will remain set in the current scope.

A bit more complicated than I thought, but works like a charm! Thanks so much!! — BrainStone, Aug 01 '18 at 14:36

score 0 · Answer 2 · answered Jul 06 '22 at 16:08

Another solution using expkv with the expkv-def front end.

This solution uses a group to keep the effects of the key=value argument local. If using a group isn't possible for other reasons you could as well set flag=false before evaluating #1 in the \ekvset-call.

\documentclass{article}
\usepackage{expkv-def}
\ekvdefinekeys{brainstone}
  {
    boolTF flag = \brainstoneFlag
  }
\NewDocumentCommand\brainstone{O{}}
  {%
    \begingroup % group keeping the changes local
      \ekvset{brainstone}{#1}%
      The flag is set to \brainstoneFlag{true}{false}.%
    \endgroup
  }
\begin{document}
\brainstone
\brainstone[flag=false]
\brainstone[flag]
\brainstone[flag=true]
\end{document}

Define Command/Macro with boolean flag

2 Answers2

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