markdown environment inside beamer frame

[Ninlives]

The following snippet will not work:

\begin{frame}
\begin{markdown}
- A markdown list
\end{markdown}
\end{frame}

and end with the following error:

Runaway argument?
! Paragraph ended before ^^M was complete.
<to be read again>
                   \par
l.69 \end{frame}
?
! Emergency stop.
<to be read again>
                   \par
l.69 \end{frame}

Why is that? I'm unfamiliar with latex internals and I'm not sure what is going on here...

[Witiko]

@Ninlives Hi, thanks for using the Markdown package.

The following snippet will not work:

You may need to use the fragile option on your frame:

\begin{frame}[fragile]
\begin{markdown}
- A markdown list
\end{markdown}
\end{frame}

Why is that?

Both frame and markdown are buffered environments, i.e. all text inside of them is read into a variable first and only then processed by TeX. However, whereas frame buffers the text as TeX would, i.e. \command is recognized as a command, markdown uses a different catcode regime, where most of the text is kept as-is, i.e. \command is recognized as regular text. Once a text has been buffered by frame, it cannot be correctly re-read by markdown.

Specifying the fragile option informs frame that it should tread carefully and store the text into an external file instead of trying to store it in a variable. This more roundabout way causes markdown and other buffered environments such as verbatim to work fine.

[Ninlives]

Thanks, this saves my problem, though I don't quite understand the reason 😕

[Witiko]

Glad to have helped. Sorry that I couldn't explain it better, perhaps the beamer documentation can do a better job: