Using StateT with Haskeline

Main.hs

-- A receipe for using StateT with haskeline's InputT transformer.
-- Derived from this /r/haskell post: http://www.reddit.com/r/haskell/comments/1os0yq/haskeline_woes/
--
-- The key is using Control.Monad.State.Strict - using .Lazy doesn't work.

import Control.Monad.State.Strict
import Control.Monad.Trans (lift)
import System.Console.Haskeline

main =  runStateT (runInputT defaultSettings loop) ""

check ma b fb = maybe b fb ma

loop = do
   minput <- getInputLine "% "
   check minput (return ()) $ \inp -> do
     let args = words inp
     case args of
       ("quit":_)  -> do outputStrLn "quitting"; return ()
       ("set":v:_) -> do outputStrLn $ "setting value to " ++ show v; lift $ put v; loop
       ("get":_)   -> do v <- lift get; outputStrLn $ "the value is " ++ show v; loop
       _           -> do outputStrLn "huh?"; loop