Why don't those non-alphanumeric chars (*/_) get colored in blue, here?

Question

Consider the following example:

\documentclass{article}

\usepackage{listings}
\usepackage{xcolor}

\lstset{language=R,
    morecomment=[l]{>},
    commentstyle=\color{blue},
    alsoletter={*}
    }
\begin{document}

\begin{lstlisting}
> q_A=0:6
> q_B=6-q_A
> N_A=6
> N_B=4
> (factorial(q_A+N_A-1)/(factorial(q_A)*factorial(N_A-1)))
[1]   1   6  21  56 126 252 462
\end{lstlisting}

\end{document}

The above code compiles to a simplified version of the image below (from the main document):

When compiling this, the asterisk *, the underscore _, and the slash / are all still treated as special characters that should not be highlighted. I've already included the alsoletter key to include e.g. *, but the key seems to be ignored. How can I get the entire line starting with a > to be blue?

I've already checked e.g. How can I get identifier style to apply to '%' (in a Perl listing)? for special identifiers, but that doesn't seem to work here. Neither does the "normal" approach of simply using alsoletter=* or alsoletter={/}, etc.

Where is it going wrong?

Answer 1

The problem comes from how the listings language for R is defined. If you look up the definition in lstdvrs.dtx (search for \lst@definelanguage{R}), you'll see that *, /, and _ are all defined as "otherkeywords":

otherkeywords={!,!=,~,$,*,\&,\%/\%,\%*\%,\%\%,<-,<<-,_,/},%

I refer you to this other answer of mine to understand why this is problematic, and what can be done about it.

I don't think you actually want to declare * as a "letter", here (at least, that's not necessary for * to be coloured in blue like the rest of the line). There are nasty side effects to that; see the side note in https://tex.stackexchange.com/a/164634/21891.

\documentclass{article}

\usepackage{listings}
\usepackage{xcolor}

\lstset{
    language=R,
    otherkeywords={},
    otherkeywords={!,!=,~,$,\&,\%/\%,\%*\%,\%\%,<-,<<-},
    morecomment=[l]{>},
    commentstyle=\color{blue},
}
\begin{document}

\begin{lstlisting}
> q_A=0:6
> q_B=6-q_A
> N_A=6
> N_B=4
> (factorial(q_A+N_A-1)/(factorial(q_A)*factorial(N_A-1)))
[1]   1   6  21  56 126 252 462
\end{lstlisting}

\end{document}