G'day all.
Quoting Conor McBride
Where now? Well, counterexample fiends who want to provoke Oleg into inventing a new recipe had better write down a higher-order example. I just did, then deleted it. Discretion is the better part of valour.
Thankfully, I'm the sort of person who doesn't know when to stop. Is this the sort of thing you had in mind? << -- WARNING: This code is untested under GHC HEAD data State s a = Bind :: State s a -> (a -> State s b) -> State s b | Return :: a -> State s a | Get :: State s s | Put :: s -> State s () instance Monad (State s) where (>>=) = Bind return = Return instance MonadState s (State s) where get = Get put = Put runState :: State s a -> s -> (s,a) runState (Return a) s = (s,a) runState Get s = (s,s) runState (Put s) _ = (s,()) runState (Bind (Return a) k) s = runState (k a) s runState (Bind Get k) s = runState (k s) s runState (Bind (Puts) k) _ = runState (k ()) s runState (Bind (Bind m k1) k2) s = runState m (\x -> Bind (k1 x) k2) s
Cheers, Andrew Bromage