[Haskell-cafe] The Layout Rule

I am looking for background material on how GHC and other Haskell compilers implement the layout rule. Are there any papers, documentation, commentary, etc. that discus the actual implementation of this rule (even if only a paragraph or two)? I've already looked at the parsing code in GHC and UHC. Do any other Haskell compilers have interesting approaches for implementing the layout rule? I am writing a paper about a new formalism for indentation sensitive languages and I want to ensure I've covered the appropriate background material on existing implementations of the layout rule. Michael D. Adams mdmkolbe@gmail.com