[Haskell-cafe] Re: Impredicativity confusion

Dimitrios Vytiniotis wrote:

I hope this helps more than confuses, It really does, thank you. To understand your explanation completely I have to study 'Boxy types' paper thoroughly, but from the user's point of view everything is clear - GHC currently cannot correctly instantiate type variables in polymorphic function's type when some of arguments have polymorphic types and only types of arguments are given.