main :: IO()
 main = runInputT defaultSettings loop
 where
   --loop :: InputT IO ()
   loop = do
     minput <- getInputLine "$ "
     case minput of
       Nothing -> return ()
       Just input -> process $ words input
     loop

process :: [String] -> IO ()

• Couldn't match type ‘IO’ with ‘InputT m’
Expected type: InputT m ()
  Actual type: IO ()
• In the expression: process $ words input
In a case alternative: Just input -> process $ words input
In a stmt of a 'do' block:
  case minput of {
    Nothing -> return ()
    Just input -> process $ words input }