Dear cafe, I am writing a library for parsing higher-kinded data, based on the czipwith package [1]. I ran into the following problem. I have a type class class Config p f | f -> p where f :: (* -> *) -> * is the higher-kinded data and p :: * -> * is the associated parser type. I want to add a class member that does not mention f in its type, e.g. heading :: p String Naturally, this would lead to ambiguity checks to fail, as the usage of heading does not tell which Config instance to use. My usual workaround would be to wrap `heading` in a phantom type, e.g. data Heading f p = Heading (p String) and give `heading` the type Heading f p. However, ghc-8.0.2 complains about f not being a type: • Expecting one more argument to ‘f’ Expected a type, but ‘f’ has kind ‘(* -> *) -> *’ • In the first argument of ‘Heading’, namely ‘f’ In the type signature: heading :: Heading f p In the class declaration for ‘Config’ Is there a restriction of the kinds that can be used in parametric types? Cheers, Olaf [1] http://hackage.haskell.org/package/czipwith