How to define a key=value that has an equivalent boolean value key

Question

Assume you're defining a key=value align for some environment realign that you'll use in the following way:

\usepackage{xkeyval}% http://ctan.org/pkg/xkeyval
\newenvironment{realign}[1][]
  {\setkeys{fam}{#1}\myalignment}% \begin{realign}
  {}% \end{realign}

You define the align choice key to set \myalignment by using (taken from the xkeyval documentation):

\define@choicekey*{fam}{align}[\val\nr]{left,center,right}{%
  \ifcase\nr\relax
    \def\myalignment{\raggedright}% align=left
  \or
    \def\myalignment{\centering}% align=center
  \or
    \def\myalignment{\raggedleft}% align=right
  \fi
}

However, now you have the awesome idea of creating corresponding boolean keys left, center and right such that left|center|right=true is equivalent to align=left|center|right. Is it possible to define the boolean keys inside a macro definition, for example, via something like \newboolkey{left}:

\newcommand{\newboolkey}[1]{
  \define@boolkey{fam}[@bool@]{#1}[true]{%
    \csname if@bool@#1\endcsname%
      \setkeys{fam}{align=#1}%
    \fi%
  }%
}

This doesn't work, since the argument #1 of \newboolkey doesn't translate properly to the definition of the left key.

Of course, removing \define@boolkey from \newboolkey and explicitly stating the key (instead of #1) works. However, I'm not interested in creating a boolean key in this way (by hand). I'd like to use a macro definition to do this since it should be automated and flexible.

Here's a non-working minimal example:

\documentclass{article}
\usepackage{lipsum}% http://ctan.org/pkg/lipsum
\usepackage{xkeyval}% http://ctan.org/pkg/xkeyval
\newenvironment{realign}[1][]
  {\setkeys{fam}{#1}\myalignment}% \begin{realign}
  {}% \end{realign}
\makeatletter
\define@choicekey*{fam}{align}[\val\nr]{left,center,right}{%
  \ifcase\nr\relax
    \def\myalignment{\raggedright}% align=left
  \or
    \def\myalignment{\centering}% align=center
  \or
    \def\myalignment{\raggedleft}% align=right
  \fi
}
\newcommand{\newboolkey}[1]{
  \define@boolkey{fam}[@bool@]{#1}[true]{%
    \csname if@bool@#1\endcsname%
      \setkeys{fam}{align=#1}%
    \fi%
  }%
}

\makeatother
\begin{document}
\begin{realign}[align=left]
\lipsum[1]
\end{realign}

\newboolkey{left}% Create a boolean equivalent for align=left
\makeatletter
\if@bool@left\else% Check if key is defined.
  \texttt{left} key defined
\fi

\begin{realign}[left]% Doesn't work
\lipsum[1]
\end{realign}
\end{document}

Answer 1

Marco's already posted a version, but this is I think a bit closer to what you were trying, just fixed the #1/##1 confusion.

\documentclass{article}
\usepackage{lipsum}% http://ctan.org/pkg/lipsum
\usepackage{xkeyval}% http://ctan.org/pkg/xkeyval
\newenvironment{realign}[1][]
  {\let\myalignment\relax\setkeys{fam}{#1}\myalignment}% \begin{realign}
  {}% \end{realign}
\makeatletter
\define@choicekey*{fam}{align}[\val\nr]{left,center,right}{%
  \ifcase\nr\relax
    \def\myalignment{\raggedright}% align=left
  \or
    \def\myalignment{\centering}% align=center
  \or
    \def\myalignment{\raggedleft}% align=right
  \fi
}
\newcommand{\newboolkey}[1]{
  \define@boolkey{fam}[@bool@]{#1}[true]{%
    \csname if##1\endcsname
      \setkeys{fam}{align=#1}%
    \csname fi\endcsname
  }%
}

\makeatother
\begin{document}
\begin{realign}[align=left]
\lipsum[1]
\end{realign}

\newboolkey{left}% Create a boolean equivalent for align=left
\makeatletter
\if@bool@left\else% Check if key is defined.
  \texttt{left} key defined
\fi

\begin{realign}[left]% Doesn't work
\lipsum[1]
\end{realign}
\end{document}

Answer 2

You can test the argument of define@boolkey. It's easier to handle:

\newcommand{\newboolkey}[1]{%
  \define@boolkey{fam}[@bool@]{#1}[true]{%
   \in@{true}{##1}
   \ifin@
     \setkeys{fam}{align=#1}%
  \fi
  }%
}

If you want to use your code you can use:

\newcommand{\newboolkey}[1]{
  \define@boolkey{fam}[@bool@]{#1}[true]{%
    \csname if@bool@#1\endcsname%
      \setkeys{fam}{align=#1}%
    \csname  fi \endcsname%
  }%
}

The complete code which works for me:

\setcounter{errorcontextlines}{999}
\documentclass{article}
\usepackage{lipsum}% http://ctan.org/pkg/lipsum
\usepackage{xkeyval}% http://ctan.org/pkg/xkeyval
\newenvironment{realign}[1][]%
  {\setkeys{fam}{#1}\myalignment}% \begin{realign}
  {}% \end{realign}
\makeatletter
\let\myalignment\relax
\define@choicekey*{fam}{align}[\val\nr]{left,center,right}{%
  \ifcase\nr\relax
    \def\myalignment{\raggedright}% align=left
  \or
    \def\myalignment{\centering}% align=center
  \or
    \def\myalignment{\raggedleft}% align=right
  \fi
}
\newcommand{\newboolkey}[1]{%
  \define@boolkey{fam}[@bool@]{#1}[true]{%
   \in@{true}{##1}
   \ifin@
     \setkeys{fam}{align=#1}%
  \fi
  }%
}

\makeatother
\begin{document}
\begin{realign}[align=center]
\lipsum[1]
\end{realign}

\hrulefill

\newboolkey{left}% Create a boolean equivalent for align=left



\begin{realign}[left]
\lipsum[1]
\end{realign}
\end{document}

Answer 3

I saw that you wanted to define more than one boolean key. I decided to use ltxkeys package. I would have used key environment for this task, but here is what you wanted. I would also first have thought of the command \ltxkeys@declarekeys.

\documentclass{article}
\usepackage{lipsum}
\usepackage{ltxkeys}
\makeatletter
\newenvironment{realign}[1][]{%
  \let\myalignment\relax
  \ltxkeys@setkeys[WN]{fam}{#1}\myalignment
}{}
% 1. The *-form of \ltxkeys@choicekey will convert the user input to lowercase 
%    before checking the value against the nominations and executing the callbacks.
% 2. The !-form will fully expand the user input before checking it against
%    the nominations.
% 3. The +-form expects two callbacks (one for when the user input is valid,
%    and the other for when the user input isn't in the nominations).

% \val and \mpcalign hold the same content.
\ltxkeys@choicekey*+![WN]{fam}[mpc]{align}[\val\nr]{%
  center/.code=\let\myalignment\centering,
  left/.code=\let\myalignment\raggedright,
  right/.code=\let\myalignment\raggedleft
}[center]{%
  % Callback for when value is correct, ie, in the list {left,right,center}.
}{%
  \@latexerr{Invalid value for key 'align'}\@ehd
}
% I thought you meant to define more than one boolean key:
\ltxkeys@boolkeys[WN]{fam}[mpb]{left,right,center}[true]{%
  \ifboolFT{mpb\ltxkeys@tkey}{}{%
    \cptexpanded{\ltxkeys@setkeys[WN]{fam}{align=\ltxkeys@tkey}}%
  }%
}
\let\ltxsetkeys\ltxkeys@setkeys
\makeatother
\begin{document}
\begin{realign}[align=left]
\lipsum[1]
\end{realign}
\begin{realign}[align=right]
\lipsum[1]
\end{realign}
\ltxsetkeys[WN]{fam}{right=true}
\ltxsetkeys[WN]{fam}{left=false}
\def\say#1{%
  \cptdocommalist{#1}{%
    \endgraf Key \texttt{##1} set
    \ifboolTF{mpb##1}{true}{false}.
  }%
}
\say{left,right,center}
\end{document}