Ending an environment in the 'before' of a new environment

Question

I'm trying to create an environment that will close a multicols group, do a thing, then start a new multicols.

Something like

\newcount{\colcount}
\newenvironment{balancedbreak}{%
\let\colcount\col@number
\end{multicols}\newpage\begin{multicols}{\colcount}
}{
}

This does not work, I get the error message

! LaTeX Error: \begin{balancedbreak} on input line 38 ended by \end{multicols}

MWE

This builds.

\documentclass{article}
\usepackage{multicol}
\usepackage{lipsum}

\newcount{\colcount}
\newenvironment{balancedbreak}{%
\let\colcount\col@number%
%\end{multicols}\newpage\begin{multicols}{\colcount}%
\newpage
}{%
}

\begin{document}
\begin{multicols}{2}
\lipsum[1]
\lipsum[2]
\begin{balancedbreak}
\textbf{Testing here}
\end{balancedbreak}
\lipsum[3]
\lipsum[4]
\end{multicols}
\end{document}

I get one long unbalanced column, then a new page and balanced columns. If I uncomment the line starting \end{multicols} in the new environment and comment out the next one I get the error message above.

I'm curious about the general case: "how do I end an environment in the 'before' section of a \newenvironment?

(My immediate need is "how can I better achieve the goal of ending a multicols page so it balances and move to the next page?". I could simply not do it at all the way I am now, but I'd like to use an environment for other reasons.)

Answer 1

It would be a whole lot easier to do this with a macro. With an environment you have to keep track of \@currenvir and to be in the right group. The \endgroup and \begingroup are to terminate and restart the blanacedbreak environment.

\documentclass{article}
\usepackage{multicol}
\usepackage{lipsum}
%\tracingmacros=1

\makeatletter
\newcount{\colcount}
\newenvironment{balancedbreak}{%
\global\colcount=\col@number% current value will otherwise be lost
\endgroup\endmulticols\newpage
\multicols\colcount\begingroup
\def\@currenvir{balancedbreak}%
}{}%
\makeatother

\begin{document}
\begin{multicols}{2}
\lipsum[1]
\lipsum[2]
\begin{balancedbreak}
\textbf{Testing here}
\end{balancedbreak}
\lipsum[3]
\lipsum[4]
\end{multicols}
\end{document}

Answer 2

Further research and experimentation show that the new environment is not just a 'wrapper for stuff', but actually has structural meaning (creates a implicit group). That is,

\newcount\colcount
\newenvironment{balancedbreak}{%
\let\colcount\col@number%
\end{multicols}\newpage\begin{multicols}{\colcount}%
}{%
}

acts something like

• \begin{balancedbreak}
  • \begingroup
    • \let\colcount\col@number
    • \end{multicols}\newpage\begin{multicols}{\colcount}

I'd thought -- incorrectly, it seems -- that the 'before' was something like a text substitution. I'd forgotten the implicit begingroup.

It turns out that using the definition above,

\balancedbreak
Some content goes here
\endbalancedbreak

Does appear to work.

Current working solution:

\newcount\colcount
\newenvironment{balancedbreak}{%
\ifnum\doublecol@number>\z@ % if multicol
  \let\colcount\col@number%
  \end{multicols}\newpage\begin{multicols}{\colcount}%
\else%
  \newpage%
\fi
}{%
}

This works if and only if there is no other \begin{someenv} between the \begin{multicols} and the \balancedbreak. There can be a \begin{someenv} some stuff goes here \end{someenv} without a problem, but this cannot happen 'inside' another environment or group.

This is way more brittle than really makes me happy, and I don't know that I'd recommend it as a general solution. That said, understanding how it works and why, I think I can live with it. I am, of course, open to other solutions.