hyphenation of text within math

Question

I would like text like

\((\abcdefghij,\abcdefghij)\)-pair

(with \abcdefghij defined as \textit{abc\-defg\-hij}) to be hyphenated as

(abc·defg·hij,·abc·defg·hij)-·pair

("·" indicates all possible linebreak points; there would of course need to be hyphens if the adjacent characters on both sides are letters). Let's assume that I need a macro like \abcdefghij in many places in the document. How can I achieve the intended hyphenation?

Answer 1

Hyphenation works in math as long as you are not inside a {} group which is essentially an \hbox in math mode. \begingroup groups are OK though.

As you did not provide a MWE (grumble) I stole one from Hendrik's answer.

\documentclass{article}
\newcommand*\abcdefghij{%
  \begingroup\mathit{\xdef\tmp{\fam\the\fam\relax}}\tmp
  abc\-defg\-hij\endgroup}

\begin{document}
\noindent
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and to end with, one last
\((\abcdefghij,\abcdefghij)\)-pair.
\end{document}

Answer 2

One way to achieve the intended hyphenation is to put the "syllables" into separate \textit commands, separated by discretionary breaks \-. (This interferes with the kerning in abcdefghij, but works reasonably well.) To allow a line break after the comma, you can use the code from this answer by egreg.

Note that I put an italic correction \/after the j so that it's not that close to the closing parenthesis anymore.

\documentclass{article}
\newcommand*\abcdefghij{\textit{abc}\-\textit{defg}\-\textit{hij\/}}
\AtBeginDocument{%
  \mathchardef\mathcomma\mathcode`\,
  \mathcode`\,="8000 
}
{\catcode`,=\active
  \gdef,{\mathcomma\discretionary{}{}{}}
}
\begin{document}
\noindent
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and a 
\((\abcdefghij,\abcdefghij)\)-pair and to end with, one last
\((\abcdefghij,\abcdefghij)\)-pair.
\end{document}