@hackage preprocessor-tools2.0.2

This library provides a quick-and-dirty (but often effective) method for extending Haskell's syntax using a custom preprocessor. It parses Haskell into a bare-bones AST with just enough knowledge of the syntax to preserve nesting, and then allows transformations on the AST.

See the package ixdopp (http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ixdopp) for an example of how to do this.