Strange listings, minipage and newcommand interaction

Question

I like to define the following command :

\newcommand{\page}[2]{\begin{minipage}{#1\textwidth} #2 \end{minipage}}

So that I can do stuff like

\page{0.1}{blabla}\page{0.3}{lalala}

I've recently discovered the package listings and I've noticed a very strange interaction.

This code doesn't trigger any error :

\begin{minipage}{0.5\textwidth}
\begin{lstlisting}  
    bla bla
\end{lstlisting}
\end{minipage}

But this :

\page{0.5}{
\begin{lstlisting}  
    bla bla
\end{lstlisting}
}

throws : Emergency stop. [...] job aborted, no legal \end found

And I must say I'm very confused, since I do not see much difference between those two.

Answer 1

If you define our \page macro using directly primitive commands (\vtop or \vbox), then you will not have problem with verbatim environment inside \page parameter:

\documentclass{article}

\def\page#1{\vtop\bgroup \hsize=#1\hsize \let\next}

\begin{document}

\page{0.5}{
\begin{verbatim}
bla bla
\end{verbatim}
}

\end{document}