Listings “cannot load requested language”

Question

If my understanding that it is possible to specify the programming language for the listings globally as well as on the listing by listing basis is correct, than the following should work:

\documentclass[11pt,letterpaper]{book}
\usepackage{listings}

\begin{document}

\lstloadlanguages{SQL,Basic} %Listings manual, pp. 11, 13
\lstset{
     frameround=fttt
    ,language=SQL
    ,numbers=left
    ,breaklines=true
    ,showstringspaces=false
    ,basicstyle=\small
}

\begin{lstlisting}[language=Basic,label={lst:ssrscurmon}]
=MonthName(DatePart(DateInterval.Month, Today()))
\end{lstlisting}

\end{document}

But it instead throws

Package Listings Error: Couldn't load requested language \lstloadlanguages{SQL,Basic}

How can I specify Basic for some listings in the document, where the majority are in SQL?

Answer 1

This can be considered a bug in listings; in lstdvrs.dtx, more specifically.

The lstdvrs.dtx file is where all listings languages and dialects are defined. In particular, a language called Basic (together with only one dialect, Visual) is defined there.

The problem is that, even though the Basic language comes with only one dialect (Visual), the default dialect for Basic is defined nowhere in lstdvrs.dtx. Therefore, if you simply specify

language=Basic

listings has no clue which language you're referring to! The same problem arises, for the same reason, if you try to load the Assembler language without also specifying a dialect.

To fix the problem, you have two options:

1. Whenever you want to use Basic, specify its only dialect (Visual) also:

   language={[Visual]Basic}
   

2. Fix that bug in listings yourself by defining the default dialect for Basic:

   \lstset{defaultdialect=[Visual]Basic}
   

   (As Peter notes, this should preferably be done in your preamble. You should endeavour to separate style from content; the former should go in the preamble, whereas the latter should go in the body of your document.)

   Then you should be able to use the Basic language without mishap. No need to use \lstloadlanguages at all (although, as pointed out by Peter, you may still want to load the languages you use right after loading the listings package, for efficiency reasons; see the note at the bottom of section 2.2 in the documentation).

---

\documentclass[11pt,letterpaper]{book}

\usepackage{listings}
\lstset{
    defaultdialect=[Visual]Basic
    ,frameround=fttt
    ,language=SQL
    ,numbers=left
    ,breaklines=true
    ,showstringspaces=false
    ,basicstyle=\small
}

\begin{document}

\begin{lstlisting}[language=Basic,label={lst:ssrscurmon}]
=MonthName(DatePart(DateInterval.Month, Today()))
\end{lstlisting}

\end{document}

Answer 2

As you can see on Table 1 (page 13) of the listings documentation, only Visual Basic is supported; this can also be seen in the file lstlang1.sty, where you find the definition

\lst@definelanguage[Visual]{Basic}
  {
  ...
  }

You need the to load [Visual](Basic); the complete code:

\documentclass[11pt,letterpaper]{book}
\usepackage{listings}

\lstloadlanguages{SQL,[Visual]Basic} %Listings manual, pp. 11, 13
\lstset{
     frameround=fttt
    ,language=SQL
    ,numbers=left
    ,breaklines=true
    ,showstringspaces=false
    ,basicstyle=\small
}

\begin{document}

\begin{lstlisting}[language={[Visual]Basic},label={lst:ssrscurmon}]
=MonthName(DatePart(DateInterval.Month, Today()))
\end{lstlisting}

\end{document}

The output: