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
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