Listings: overloaded use of dash

Question

In my language, I use the dash character - in three different contexts.

As an operator, e.g., 5 - 1.
As a minus sign, e.g., -10.
As part of a keyword, e.g., some-keyword.

I would like to have a different style for each of these. Is this possible?

What I tried so far. Let me start from the most naive minimal example.

\documentclass{article}
\usepackage{listings}
\usepackage{xcolor}
\lstdefinelanguage{MyLang}{
keywords={},
otherkeywords={+,-}, % operators
morekeywords=[2]{akeyword, other-keyword}, % keywords
}
\lstset{
  keywordstyle=\color{magenta}, % operators
  keywordstyle=[2]{\color{violet}}, % keywords
  language=MyLang
}
\begin{document}
\begin{lstlisting}
5 - 1 + -10   akeyword   some-keyword
\end{lstlisting}
\end{document}

This results in all dashes being styled as an operator. However, I would like the second dash to be rendered black, and the third one purple. Note that the keyword containing a dash is not recognized at all.

For the minus sign, I found a workaround using the literate option of listings. For example, by adding literate={_}{\textminus}1, to the language definition, I can rewrite the example program as 5 - 1 + _10 akeyword some-keyword which results in the following.

Of course, this is not ideal, because I have to replace each minus sign with an underscore manually, but in my case I find this acceptable. Still, bonus points if there is a solution for this. :)

For the keyword, I understood from this answer that adding alsoletter=-, should do the trick, but this does not seem to work.

Your some-keyword isn't highlighted even if you use alsoletter=- because your language setup uses other-keyword (which isn't the same). — Skillmon, Dec 08 '21 at 16:16

score 2 · Accepted Answer · answered Dec 08 '21 at 16:12

By using alsoletter={-} the - is considered a letter. This way things like -1 (or any number) become an unknown keyword, so aren't highlighted as a single keyword. Also, this way it can be used in the middle of another keyword you want to define with morekeywords:

\documentclass{article}
\usepackage{listings}
\usepackage{xcolor}
\lstdefinelanguage{MyLang}{
alsoletter={-},
keywords={-}, % operators
otherkeywords={+},
keywords=[2]{akeyword,some-keyword}, % keywords
}
\lstset{
  keywordstyle=[1]\color{magenta}, % operators
  keywordstyle=[2]{\color{violet}}, % keywords
  language=MyLang
}
\begin{document}
\begin{lstlisting}
5 - 1 + -10   akeyword   some-keyword
\end{lstlisting}
\end{document}

Caveat: In 5-1 the - will not be highlighted as a binary operator (you need spaces).

Output:

Wow, and now that I added this answer I read the last part of your question and see you already considered alsoletter... Well, here is how you should use it! — Skillmon, Dec 08 '21 at 16:15

Listings: overloaded use of dash

1 Answers1