[Haskell] pretty-printing Haskell with automatic parens?

The haskell-src package contains a pretty-printer for Haskell syntax that requires parentheses to be explicitly placed in the (abstract) syntax representation. I have some code for automatically inserting parentheses where necessary (for use before pretty-printing), but I'm guessing someone else has done so better than I. Does anyone have pointers? I'm glad to share my version as well. Cheers, - Conal