\documentclass{article}
\begin{document}
\begin{haskellpragmas}
{-# LANGUAGE OverloadedStrings #-}
\end{haskellpragmas}
\begin{writehaskell}
import Text.LaTeX

overloaded :: LaTeX
overloaded = "This is an Overloaded String."
\end{writehaskell}
\hatex{overloaded}
\end{document}