On Thu, Apr 17, 2003 at 09:02:45AM +0100, Simon Peyton-Jones wrote:
data T = forall a. Foo a (a -> Int)
I find this perfectly acceptable and consistent. The right hand side of a data type declaration lists the ways to construct an element of the data type. I read data List a = Cons a (List a) | Nil as "To construct an element of type 'List a', you can either build a Cons from an 'a' and a 'List a', or you can build a Nil." So likewise, data T = forall a. Foo a (a -> Int) reads as "To construct an element of type 'T', you can, for all types 'a', build a Foo from an 'a' and a 'a -> Int'. An "exists" quantifier would make sense for real existential _types_: data T = Foo (exists a . (a, a -> Int)) but for the current use, "forall" is quite appropriate, in my opinion. Lauri Alanko la@iki.fi