Why is the `pgffor` package messing with my scope?

Question

I have a several rather lengthy documents with numbered points (catechism questions) that I would like to be able to selectively include in other documents using a utility function that uses a range argument. I ran into trouble and eventually traced it to the way the \foreach seems to run in its own private scope of some kind. The loops seem to iterate properly, but things set inside them (such as \newif definitions or toggles from the etoolbox package don't seem to stick.

This fails miserably:

\documentclass{scrartcl}
\usepackage{pgffor}
\usepackage{etoolbox}

\newcommand{\wkk}[1]{%
    \foreach \x in {1,...,5}{%
        \providetoggle{wkk\x}
    }
    \foreach \x in {#1}{%
        \toggletrue{wkk\x}
    }
    % In a real example the following content would be \input here
    \iftoggle{wkk1}{output 1 }{}
    \iftoggle{wkk2}{output 2 }{}
    \iftoggle{wkk3}{output 3 }{}
    \iftoggle{wkk4}{output 4 }{}
    \iftoggle{wkk5}{output 5 }{}
}

\begin{document}

\wkk{2,...,4}

\end{document}

Yet if I replace the \foreach loops with exactly what they should be doing in the above example, it works fine:

\documentclass{scrartcl}
\usepackage{pgffor}
\usepackage{etoolbox}

\newcommand{\wkk}[1]{%
    \providetoggle{wkk1}
    \providetoggle{wkk2}
    \providetoggle{wkk3}
    \providetoggle{wkk4}
    \providetoggle{wkk5}
    \toggletrue{wkk2}
    \toggletrue{wkk3}
    \toggletrue{wkk4}
    % In a real example the following content would be \input here
    \iftoggle{wkk1}{output 1 }{}
    \iftoggle{wkk2}{output 2 }{}
    \iftoggle{wkk3}{output 3 }{}
    \iftoggle{wkk4}{output 4 }{}
    \iftoggle{wkk5}{output 5 }{}
}

\begin{document}

\wkk{2,...,4}

\end{document}

Obviously these are kind of clumsy MWE's and I would be including the content from an external source file that was marked up with the correct toggles.

What am I doing wrong with the pgffor package? Or is there a conceptually better way to do this?

Answer 1

Each cycle of \pgffor is performed in a group, so the definition of the toggles and the setting don't survive them.

One can solve the issue with \toggletrue by writing \global\toggletrue, but there's no “global \providetoggle”. However you can define your own:

\let\gprovidetoggle\providetoggle
\patchcmd{\gprovidetoggle}{\cslet}{\global\cslet}{}{}

Example:

\documentclass{scrartcl}
\usepackage{pgffor}
\usepackage{etoolbox}

\let\gprovidetoggle\providetoggle
\patchcmd{\gprovidetoggle}{\cslet}{\global\cslet}{}{}

\newcommand{\wkk}[1]{%
    \foreach \x in {1,...,5}{%
        \gprovidetoggle{wkk\x}%
        \global\togglefalse{wkk\x}% set it to false
    }%
    \foreach \x in {#1}{%
        \global\toggletrue{wkk\x}%
    }%
    % In a real example the following content would be \input here
    \iftoggle{wkk1}{output 1 }{}%
    \iftoggle{wkk2}{output 2 }{}%
    \iftoggle{wkk3}{output 3 }{}%
    \iftoggle{wkk4}{output 4 }{}%
    \iftoggle{wkk5}{output 5 }{}%
}

\begin{document}

\wkk{2,...,4}

\end{document}