Yay_Reader.hs

instance (Monad m) => Monad (ReaderT r m) where
      return   = lift . return

      (>>=) :: ReaderT r m a -> (a -> ReaderT r m b) -> ReaderT r m b
      (ReaderT rma) >>= k  = ReaderT $ \ r -> do
          a <- rma r
          let ReaderT rmb = k a -- rmb :: r -> m b
          rmb r :: m b          -- rmb r ::    m b

ask :: Monad m => (ReaderT r m) r == (r -> m r)
ask = ReaderT return