Hi Roel Thanks for the information. With Precis, I wanted to make a standalone tool rather than work with GHC-API. I don't know how stable GHC-API, but I expect it to be less stable than haskell-src-exts, and as Precis is a tool to help gauge the stability of packages I want it to be stable itself. Certainly, I don't want to be committed to getting it to work with each GHC revision. The downside to this that Precis will always lack some of the power that it could get from GHC-API. Modules with inline FFI code won't parse, and evidently Unicode symbols don't parse either. Also, even after a successful parse, the analysis that Precis does is quite shallow, diffs are calculated by pretty printing the AST of the relevant constructions (module export lists, type signatures of functions/constants..., class instances, data and class declarations). Because the analysis is shallow - quite a few false positives are generated. Changing say a type alias will indicate a change, e.g. the code below will indicate a change but the change shouldn't merit a major version number change: doesFileExist :: FilePath -> IO Bool doesFileExist :: String -> IO Bool This is the reason I stop short of considering Precis a Package Version Policy checker and only report numbers of apparent changes not a conclusion drawn from them, as I think Henning suggested. From the work done to get Precis where it is, I'd wager trying to build a fully automatic PVP checker would be more effort that its usefulness would merit. Best wishes Stephen