Hi. I'm working through "Haskell Design Patterns" and got inspired to try to create my first monad stack. What I really wanted though (not shown in the book) was to combine State and Rand. I daresay I got something to compile: walk :: RandomGen g => StateT (Float, Float) (Rand g) (Float, Float) walk = do (x, y) <- get put (x + 1, y + 1) get >>= return However, the moment I try to insert a getRandomR or something in it, I get an error Could not deduce (MonadRandom (StateT (Float, Float) (Rand g))) arising from a use of `getRandomR' <...snip...> add an instance declaration for (MonadRandom (StateT (Float, Float) (Rand g))) I see there are instances MonadRandom m => MonadRandom (StateT s m) RandomGen g => MonadRandom (Rand g) in Control.Monad.Random.Class, so I am not quite sure what is expected of me. -- http://justonemoremathproblem.com To protect my privacy, please use PGP encryption. It's free and easy to use! My public key ID is 0x340EA95A (pgp.mit.edu).