I came across something that seems a bit strange to me. Here is a simplified version (the original was trying to move from a lens ReifiedFold to a lens-action ReifiedMonadicFold) {-# LANGUAGE RankNTypes #-} import Control.Applicative newtype Wrap = Wrap { extract :: forall f. Functor f => f Int } trip :: Wrap -> Wrap trip a = Wrap (extract a) The compiler is okay with this. It chokes on this alternative though trip :: Wrap -> Wrap trip = Wrap . extract giving (GHC 7.8.2) Couldn't match type ‘f0 Int’ with ‘forall (f :: * -> *). Functor f => f Int’ Expected type: f0 Int -> Wrap Actual type: (forall (f :: * -> *). Functor f => f Int) -> Wrap In the first argument of ‘(.)’, namely ‘Wrap’ In the expression: Wrap . extract I'm guessing this is because the compiler fancy footwork to handle the implicit parameters, something like trip a = Wrap (\f fDict -> extract a f fDict) where f is the Functor type and fDict is the associated dictionary, isn't compatible with the (.) definition of f . g = \x -> f (g x) Is this correct? I would appreciate anyone insight here. Is there a way combine these (.) style? Thanks! -Tyson