I believe, Language.Haskell.Pretty can properly output haskell code (and the GHC API should be able to do so, too. Does the GHC API output tabs?)
Surely you mean Language.Haskell.Exts.Pretty, right? ;-) The haskell-src-exts library does not (yet) support full round-tripping source-to-source, so the generated output will be different from what was read. But it will at least produce valid output. Hopefully in a few months' time it will do the full round-tripping as well, at least that's the plan. In general, unless you actually want to use any other components of the GHC API, e.g. evaluate your code, then I see no reason to use the GHC API for source manipulation. haskell-src-exts simply does that better (and definitely better than haskell-src). But I couldn't tell if that's enough for the original poster's needs. :-) [/shameless plug] Cheers, /Niklas