On 2/3/13 12:27 AM, Stephen Tetley wrote:
Haskell-src-exts parses real Haskell - including most (if not all?) GHC extensions. If you were wanting to analyze 'in the wild' Haskell projects you might also want to use CPPHS as many Haskell projects use the CPP preprocessor.
That was something that surprised me when I first started using haskell-src-exts. Since haskell-src-exts parses language pragmas (including the CPP pragma), and since the haskell-src-exts package depends on the cpphs package, I'd made the assumption it would run the C preprocessor if the source file asked for the CPP language extension. So, I was surprised when it didn't; it might be worth documenting that it doesn't run CPP for you. (From reading the source, I discovered the reason it depends on the cpphs package is to run the unlit preprocessor, but not to run cpp itself.) I'm still a beginning Haskeller, so this code might be ugly, but I wrote a little bit of code to determine whether the C preprocessor was requested by the source file, and run it if necessary: stripShebang :: String -> String stripShebang ('#':'!':rest) = tail $ dropWhile (/= '\n') rest stripShebang s = s -- extension ".lhs" is same criterion haskell-src-exts uses to decide unlit perhapsUnlit fn contents = if ".lhs" `isSuffixOf` fn then unlit fn contents else contents parseFileWithCpp :: Maybe CpphsOptions -> Maybe ParseMode -> FilePath -> IO (ParseResult (Module SrcSpanInfo, [Comment])) parseFileWithCpp chopts pmode fn = do contents <- readFile fn let pmode' = fromMaybe (ParseMode fn [] False False (Just baseFixities)) pmode exts = fromMaybe [] $ readExtensions $ perhapsUnlit fn $ stripShebang contents pmode'' = if ignoreLanguagePragmas pmode' then pmode' else pmode' { extensions = nub (exts ++ extensions pmode'), -- since we already read language pragmas... ignoreLanguagePragmas = True } wannaCpp = CPP `elem` extensions pmode'' chopts' = fromMaybe defaultCpphsOptions chopts -- haskell-lang-exts already handles unlit itself, so defer to that chopts'' = chopts' { boolopts = (boolopts chopts') { literate = False } } doCpp = if wannaCpp then runCpphs else (\_ _ -> return) contents' <- doCpp chopts'' fn contents return $ parseFileContentsWithComments pmode'' contents' Although this is fairly short, it isn't entirely trivial, and since it seems like using haskell-src-exts together with cpphs is something many people would want to do, I'm wondering if I should contribute a small module to Hackage ("haskell-src-exts-cpp", perhaps) with this function and perhaps a few other functions I've discovered are useful when using haskell-src-exts. Also, just a meta-question: if I encounter bugs or want to suggest features for a package like haskell-src-exts, am I better off bringing them up on a mailing list such as this one, or should I just email the author directly? (Since haskell-src-exts, according to its Hackage page, doesn't have a bug tracker or real home page, just a darcs repository.) --Patrick