Does your pretty-printer round trip?
Absolutely. I'd think a parser that can't parse what the pretty-printer yields means you either have a broken parser or a broken pretty-printer. :-)
Except for line numbering (it inserts but doesn't read line pragmas), the AST should be preserved under f = parse . pretty.
and what about (pretty . parse) = id :: String -> String ?-) preserving everything that isn't transformed at the AST level would be a necessary starting point for refactoring larger code bases. having easy access to comments and layout information is where most frontends tend to let us down. how much of the source is preserved by (pretty . parse)? layout/comments/pragmas/.. claus ps it is good to hear that src-ext is supported, follows language developments, and is separated from the other parts of your projects!-)