gistfile1.txt

newtype ActionM a = AM { runAM :: ErrorT ActionError (ReaderT ActionEnv (StateT Response IO)) a }
    deriving ( Monad, MonadIO, Functor
             , MonadReader ActionEnv, MonadState Response, MonadError ActionError)

-- backend
get :: B.Connection -> L.Text -> ActionM (Maybe L.Text)
get b k = do
    let code = ensureUrl k
    val <- B.get b (c_of code)
    case val of
      Left e -> raise "RedisError"
      Right v -> return v

-- frontend
  get (regex "^\\/([A-Za-z0-9+\\/=]*)$") $ do
    code <- S.escape <$> param "1"
    url  <- S.get backend code