\documentclass{article}
\usepackage{color}
\usepackage{listings}

\lstdefinelanguage{ASL}
{
  morekeywords={begin,
    var,
    end},
    morecomment=[l][\color{blue}]{//},
    morecomment=[s][\color{blue}]{/*}{*/},
    morestring=[b][\color{cyan}]",
    morestring=[d][\color{cyan}]',
}
\definecolor{lightyellow}{cmyk}{0.0, 0.0, 0.20, 0.0}

\lstset{
  keywordstyle=\bf,
}

\begin{document}
Keywords un bold. Previously, only the first keyword was recognised as such when the list of key words was given with newlines after commas. For instance:
\begin{verbatim}
\lstset{
keywords={begin,
  var,
  end
}
\end{verbatim}

\begin{lstlisting}[language=ASL]
  begin
// Variable declaration   
    var x = 1;
  end
\end{lstlisting}

\begin{lstlisting}[language=Caml]
let x = 1
\end{lstlisting}
\end{document}
