Code listing with package listings

listing.tex

\usepackage{xcolor}

\definecolor{codegreen}{rgb}{0,0.5,0}
\definecolor{codegray}{rgb}{0.5,0.5,0.5}
\definecolor{backcolour}{rgb}{0.95,0.95,0.92}

\usepackage{listings}
\lstset{
  backgroundcolor=\color{backcolour},
  basicstyle=\small\sffamily,
  commentstyle=\it\color{codegray},
  stringstyle=\mdseries\rmfamily\color{codegreen},
  keywordstyle=\bfseries\rmfamily\color{codegreen},
  frame=single, % none
  xleftmargin=2pt,
  stepnumber=1,
  numbers=left,
  numbersep=5pt,
  numberstyle=\ttfamily\tiny\color[gray]{0.3},
  belowcaptionskip=\bigskipamount,
  captionpos=b,
  %escapeinside={*'}{'*},
  language=haskell,
  tabsize=2,
  emphstyle={\bf},
  columns=flexible,
  showspaces=false,
  showstringspaces=false,
  showtabs=false,                  % show tabs within strings adding particular underscores
  morecomment=[l]\%,
  rulecolor=\color{black}         % if not set, the frame-color may be changed on line-breaks within not-black text (e.g. comments (green here))
}

\begin{document}

\begin{lstlisting}
class Classifier c where
  -- | Given a training set returns a trained classifier
  train :: [(Sample, Class)] -> c
  -- | Given a random sample, predict a class
  predict :: Sample -> c -> [(Class, Probability)]
\end{lstlisting}

\end{document}