ParseAndPrettyPrint.hs

import           Control.Arrow         ((>>>))
import           Language.Haskell.Exts
import           System.Environment
import           Text.Show.Pretty      (ppShow)

headMaybe (x:_) = Just x
headMaybe _ = Nothing

main = do
    (a:_) <- getArgs
    c <- readFile a :: IO String
    let process :: String -> String
        process =
            unlines .
            filter (headMaybe >>> maybe False (/= '#')) .
            lines
        c' = process c
    let ParseOk r = parseFileContents c'
    putStrLn $ ppShow r
    putStrLn $ prettyPrint r