[Haskell-cafe] Re: Hit a wall with the type system

[Chris Smith]

I'll repeat, just for the heck of it, that what I want is a type 
something like:

   diff :: forall A a. (A :> Floating, A a) =>
               (forall b. A b => b -> b) -> b -> b

where A is quantified over all type classes, and :> denotes "is a 
superclass of".  The syntax is made up, of course, and entirely 
unworkable since (:>) is a user-definable contructor name... but that's 
the intuition anyway.

-- 
Chris Smith