I've written this cute ;-) piece of code involving an associated type synonym, {-# OPTIONS_GHC -fglasgow-exts #-} class ZipWithA a where type Elem a :: * zipWithA :: [Elem a] -> a instance ZipWithA [a] where type Elem [a] = a zipWithA xs = xs instance ZipWithA b => ZipWithA ([a] -> b) where type Elem ([a] -> b) = a -> Elem b zipWithA fs = zipWithA . zipWith ($) fs and it behaves as intended: *Main> zipWithA [2, 3] :: [Int] [2,3] *Main> zipWithA [pred, succ] [2, 3] :: [Int] [1,4] *Main> zipWithA [(+), (-)] [2, 3] [5, 7] :: [Int] [7,-4] However, as soon as the overloading cannot be resolved, the type checker loops: *Main> zipWithA [head, last] ["more than", "haskell"] :: String "ml" *Main> zipWithA [head, last] ["more than", "haskell"] <<loops>> Just to be clear, I do not expect GHC to be able to type this last example, I would just have thought it would want to tell me in finite time that it cannot resolve the overloading here. Should I report this a bug? Or is it perhaps already been taken care of in the head? Or am I just plain unreasonable here? :-) Cheers, Stefan