Hi
The top match of hoogle "(a -> b) -> b" is the inexact match
Control.Monad.State.Class.gets :: MonadState s m => (s -> a) -> m a
(which cannot be made to unify with (a -> b) -> b) instead of
Control.Monad.Cont.runCont (undefined :: Cont r a) :: (a -> r) -> r
which does.
What if the type of gets was :: (s -> a) -> m a? Would you then think it was the right choice of ordering? In runCont you are effectively deleting an argument to get equality, in gets you are simply unifying "a" and "m a". Since m a is just wrapped in a container (monad in this case), its entirely feasible the person wanted the monadic version. The reason Hoogle sees gets without the type class is because MonadState is a multi-parameter type class, and hence not Haskell 98. Hoogle simply ignores all MPTC's while doing matching. This will be fixed in Hoogle 4. Thanks Neil