specializing on existentially quantified data types

[Simon Peyton-Jones]

| class C a where ...
| data MkC = forall a . C a => MkC a
| 
| foo :: MkC -> ...
| 
| and I want to specialize foo for when the 'a' in the MkC is, say, Int.
Is
| this possible?

Not directly.  But you can say

	foo (MkC x) = foo' x

	foo' :: forall a. C a => a -> ...
	foo' x = ...
	{-# SPECIALISE foo' :: Int -> ... #-}

There's no built-in mechanism I'm afraid.

Simon