handleMsg :: Handle -> VM -> String -> IO ()
handleMsg clientHandle vm msg = do
    let splitMsg = words msg
    let action = splitMsg !! 0
    case lookup action of
        Just f  -> f clientHandle vm splitMsg
        Nothing -> putStrLn $ "unknown action " ++ action

messageHandlers :: [(String, Handle -> VM -> [String] -> IO ())]
messageHandlers = [("update",   handleUpdate),
                   ("key_down", handleKeyDown),
                   ("key_up",   handleKeyUp),
                   ("pointer",  handlePointer)]

{-----------------------------}

Main.hs:76:8:
    Couldn't match expected type `[(String, b)] -> Maybe b'
           against inferred type `Maybe a'
    In the pattern: Just f
    In a case alternative: Just f -> f clientHandle vm splitMsg
    In the expression:
        case lookup action of {
          Just f -> f clientHandle vm splitMsg
          Nothing -> putStrLn $ "unknown action " ++ (splitMsg !! 0) }