pipesGameState.hs

import Control.Monad
import Control.Applicative
import Control.Proxy
import System.IO
import Prelude hiding (Left, Right)

data Input = Up | Down | Left | Right | Invalid deriving Show

toInput :: Char -> Input
toInput c = case c of
    'u' -> Up
    'd' -> Down
    'l' -> Left
    'r' -> Right
    _   -> Invalid

inputs :: Proxy p => Handle -> () -> Producer p Input IO ()
inputs h () = runIdentityP . forever $ lift (toInput <$> hGetChar h) >>= respond

printer :: (Proxy p, Show a) => () -> Consumer p a IO r
printer () = runIdentityP . forever $ request () >>= lift . print

main = do
  hSetEcho stdin False
  runProxy $ inputs stdin >-> printer