I noticed a few bits lacking in the Control.Monad.State documentation. I think an example of using StateT to encapsulate IO would be a useful addition... In order to make StateT more interesting, the trick is to use a lift inside a function that returns StateT, so you can actually perform IO. I would guess that this is the kind of use case that most people would want to use StateT, but lift isn't mentioned in the docs. Also, the types of "runStateT" and "runState" are a little confusing, since they're actually field accessor functions, so I'd like to make a note on that. So how 'bout I add an example like the following to the State documentation? module Main where import Control.Monad.State type MyState a = StateT Int IO a stateFun :: MyState String stateFun = do modify (+100) liftIO (putStrLn "Hello!") return "foo" main = do (s, n) <- runStateT (stateFun >> stateFun) 0 putStrLn $ "n: " ++ (show n) ++ " s: " ++ s peace, isaac