The easiest way to combine State and IO is using a monad transformer. There are some lecture notes which you might find useful at http://www.md.chalmers.se/~rjmh/Combinators/Monads/index.htm which refer to a library module http://www.md.chalmers.se/~rjmh/Combinators/MonadTransformers.hs Using this library you just build the type type StateIO s a = State s IO a which is a monad with operations readState, writeState, and lift :: IO a -> StateIO s a John