Is there a switch to not echo to the console? Is this the problem? It happens in both Hugs and GHC

main :: IO ()
main = do
       putStr "sentence? "
       input <- getLine
       case input of
            "quit" -> putStr "bye.\n"
            _      -> do
                           let res = get_result $ proof $ do_proof $ getInput input
                                in if res == Nothing
                                   then putStr ("-> Nothing\n")
                                   else putStr ("-> " ++ (show $ unJust res) ++ "\n")
                                   main