\documentclass{article}

%include polycode.fmt

\newenvironment{figurehscode}
        {\(\parray}
        {\endparray\)}
\newenvironment{codefigure}
        {\begin{figure}\sethscode{figurehscode}}
        {\end{figure}}

\begin{document}

%Some text before.
\input tufte
\begin{figure}[h]
\texths

> map     ::  (a -> b) -> [a] -> [b]
> map []  =   []

\caption{Foobar}
\label{foobar}
\end{figure}
%Some text after.
\input tufte
\begin{codefigure}

> map     ::  (a -> b) -> [a] -> [b]
> map []  =   []

\caption{Foobar}
\label{foobar2}
\end{codefigure}
\input tufte


\end{document}