[Haskell-cafe] Re: GHC 6.7 and Associated Types

Maxime Henrion wrote:

class MonadState m where type StateType m :: * get :: m StateType put :: m StateType -> m ()

As for instances:

instance MonadState (State s) where type StateType = s -- this is line 22

When defining the type function StateType, you have to give it the required argument m = State s: type StateType (State s) = s

get = State $ \s -> (s, s) put s = State $ \_ -> ((), s)

Regards, apfelmus