polymorphic type in state of state monad

Hi All, Any one of your have the experience of defining a state of a state monad as a polymorphic type? I want to have:

type State = Term a => [a] data M a = M (State -> IO(State,a))

GHC yields a error message "Illegal polymorphic type". How to resolve this? Thank you very much. -W-M- @ @ | \_/