At the moment I have code like, next_random_probability :: (RandomGen g, Num a, Random a) => State g a next_random_probability = do old_rng <- get let (random_probability, new_rng) = randomR (0, 1) old_rng put new_rng return random_probability next_random_probabilityT :: (RandomGen g, Num a, Random a, Monad m) => StateT g m a next_random_probabilityT = do old_rng <- get let (random_probability, new_rng) = randomR (0, 1) old_rng put new_rng return random_probability Because these just use get and put which are both from MonadState, is it possible to write just one next_random_probability with a more general type signature, maybe mentioning MonadState, or at least two wrappers that call the same worker function, so that the same code is good for both State and StateT? -- Mark