Hallo Kiel!-)
we are trying to use the GHC API for a source-to-source transformation on Haskell programs. The result of parsing and typechecking a module enables us to apply the transformation, but writing the transformed module back using the pretty printer (Outputable) generates invalid Haskell code.
It would help to know more about your intended application. For instance, if there is a need for user-visible output, the requirements are very different from those of a simple preprocessor. In the former case, pretty-printing isn't going to get you far, even if you do write your own pretty printer - the AST doesn't have enough information to reconstruct the input program (one would need to combine the lexer's token stream with the modified AST to print out modified code - similarly to what was done in HaRe). In the latter case, you might not need to pretty-print, just modify the input before passing it on to later phases of GHC. Since you don't seem to care about formatting or comments, I suspect it is the latter - have you looked into Template Haskell as an alternative? As Thomas pointed out, there is some control over what gets qualified and what doesn't; the two indentation items you list look like plain bugs in search of a ticket and patch. Please record them on GHC's trac. Claus