existentials + contexts + universals

[Ross Paterson]

Try the following:

   data Showable = forall a. Show a => MkShowable (forall b. b -> a)

   showit (MkShowable f) = show (f 1)

and you get

   ERROR "foo.hs" (line 3): Use of MkShowable requires at least 2 arguments

Change the context to (Show a, Read a), and it wants 3 arguments, usw.