On Sun, Feb 22, 2009 at 3:17 PM, Daniel Fischer
test5b :: (Monad (StateT [Char] (StateT s m)), MonadState s (StateT s m), Num s, Monad m) => m s
Doesn't 'Monad m' imply 'MonadState s (StateT s m)' which implies 'Monad (StateT s m)' which implies 'Monad (StateT [Char] (StateT s m))'? This signature could be simplified to just test5b :: (Num s, Monad m) => m s
test5bImpl :: (Monad (StateT [Char] m), MonadState s m, Num s) => StateT [Char] m ()
Here 'MonadState s m' implies 'Monad m' which implies 'Monad (StateT [Char] m)', simplifying the signature to test5bImpl :: (Num s, MonadState s m) => StateT [Char] m () Now, note that Menendez' signatures didn't have 'Num s' because a type signature was given to 'test3' forcing the number to be Integer. If you remove all type signatures (and the monomorphism restriction), GHC 6.10 infers modifyM :: (Monad m) => (s -> m s) -> StateT s m () test3 :: (Num s, MonadState s m) => [Char] -> m [Char] test5b :: (Num b, Monad m) => m b test5b' :: (Num b, Monad m) => m b impl :: (Num s, MonadState s m) => StateT [Char] m () Did I make any mistakes? -- Felipe.