Using lhs2tex code in mathmode

codeinmath.lhs

\documentclass{article}

\usepackage{amsmath}

%include polycode.fmt

\newenvironment{autohscode}%
  {\relax\ifmmode\expandafter\pmboxed\else\expandafter\plainhscode\fi}%
  {\relax\ifmmode\expandafter\endpmboxed\else\expandafter\endplainhscode\fi}

\sethscode{autohscode}


\begin{document}

\begin{gather*}
\int_x{\left(
  \begin{code}
  foldr f z []      = z 
  foldr f z (x:xs)  = f x (foldr f z xs) 
  \end{code}
\right)}
= \mathit{nonsense}
\end{gather*}

In text mode:
\begin{code}
  foldl f z []      = z                  
  foldl f z (x:xs)  = foldl f (f z x) xs
\end{code}


\end{document}