pretty-show-1.1: ppsh.hs

import Text.Show.Pretty
import System.Environment
import System.IO(hPutStrLn,stderr)

main :: IO ()
main =
  do as <- getArgs
     case as of
       ["--test"] -> interact (show . selftest1)
       []         -> interact $ \s -> case parseValue s of
                                        Just v  -> show (ppValue v)
                                        Nothing -> s
       _ -> hPutStrLn stderr $ unlines
              [ "usage: ppsh < showed_value > pretty_value"
              , "   --test      Self test: True means we passed."
              ]

selftest :: Value -> Bool
selftest v = case parseValue $ show $ ppValue v of
               Just v1  -> v1 == v
               Nothing  -> False

selftest1 :: String -> Bool
selftest1 txt = case parseValue txt of
                  Just v  -> selftest v
                  Nothing -> True