[Haskell-cafe] RE: MPTCs and rigid variables

[David House]

On 03/03/07, C Rodrigues <red5_2 at hotmail.com> wrote:
> class Foo a b | a -> b where foo :: a -> FooBox b
> data FooBox b = forall c. Foo b c => FooBox (Maybe c)

Existential boxes is indeed the method I've used to tackle this in
practice. However, it's kind of annoying, hence my email asking
whether there's a good reason it's not possible. I guess there are no
theoretical limitations, because, as you've just shown, you can hack
your way around it.

-- 
-David House, dmhouse at gmail.com