\usepackage{listings}
\usepackage{color}

\lstnewenvironment{code}{
    \vspace{\parskip}
    \vbox\bgroup
}
{
    \egroup
    \nopagebreak[3]
}

\definecolor{shadecolor}{gray}{.96}

\lstset{
    language=Haskell,
    basicstyle=\small\tt,
    backgroundcolor=\color{shadecolor},
    showstringspaces=false,
    commentstyle={},
    frame=single,
    belowskip=0pt,
    literate=
          {-}{{$-$}}1 {+}{{$+$}}1 {/}{{$/$}}1 {*}{{$*$}}1 {=}{{$=$}}1
          {>}{{$>$}}1 {<}{{$<$}}1 {\\}{{$\lambda$}}1 {/=}{{$\neq$}}1
          {->}{{$\rightarrow$}}1 {>=}{{$\geq$}}2 {<-}{{$\leftarrow$}}2
          {<=}{{$\leq$}}2 {=>}{{$\Rightarrow$}}2
          {>>}{{>>}}2 {>>=}{{>>=}}2
}

\long\def\ignore#1{}