How to hyphenate properly at an em-dash?

Question

I am using em-dashes---for interjections---in text. Based on Why can words with hyphen char not be hyphenated? I'm using a \hyphenchar definition to let pdfTeX hyphenate words attached to em-dashes:

\documentclass{article}
\usepackage[T1]{fontenc}
\begin{document}
\hyphenchar\font=\string"7F
\parbox{1pt}{constrictions constrictions---constrictions constrictions}
\end{document}

The result is not satisfactory, though. Notice especially line 5: "s—-" where the "s" is lopped off and the em-dash is followed by a hyphen.

What I would like is a proper hyphenation of the two words attached to each em-dash, and---if necessary---to use the em-dash itself as a "hyphen" (no additional hyphen necessary if the line break occurs at the em-dash). Here I've achieved this desired result manually:

How can I get this behavior automatically?

Answer 1

You could define your own emdash command that allows a break as follows:

\newcommand{\emdash}{\nobreak---\nobreak\hskip0pt}

\documentclass{article}

\usepackage[T1]{fontenc}
\newcommand{\emdash}{\nobreak---\nobreak\hskip0pt}

\begin{document}

\parbox{1pt}{constrictions constrictions\emdash constrictions constrictions}

\end{document}