echo repl with haskeline library

echo_repl.hs

import System.Console.Haskeline
import Control.Monad 
import Control.Monad.Trans.Class
import Control.Monad.Trans.Maybe 

main :: IO ()
main = runInputT defaultSettings repl

repl :: InputT IO ()
repl = fmap (const ()) $ runMaybeT $ forever $ do
  line <- MaybeT $ getInputLine "% "
  case line of
    "quit" -> MaybeT $ return Nothing
    input  -> lift $ outputStrLn input 

needs installed haskeline(and transformers)