[jhc] explanation of FrontEnd.KindInfer.constrain

[Samuel Bronson]

On 3/18/08, John Meacham <john at repetae.net> wrote:
> On Tue, Mar 18, 2008 at 06:09:22PM -0400, Samuel Bronson wrote:
> > I don't understand how FrontEnd.KindInfer.constrain is supposed to
> > deal with KindSimple constraints... it doesn't seem to have any way of
> > replacing ?? or ? with *. Why not?
>
> that is done in the FrontEnd.Tc.Kind.kindCombine routine. The kind
> inference algorithm is based on the impredicative boxy type inferencer
> used as the main typechecker.  this is because jhc is going to be a
> kind-polymorphic system, much like the Omega language (based on
> haskell). That and I find the impredicative boxy typechecking algorithm
> quite elegant. And when my moratorium on adding new features ends, I
> want to finish support for bang kinds. so,
>
> data List a = Cons a (List a) | Nil
>
> will actualy declary a type of
>
> List :: forall (k1::**) (k2::**) . \(a::k2) -> k1
>
> (** is the supersort of boxed (but not necessarily lazy) values.
>
> this means you can have
>
> List * * - lazy list of lazy elements
> List ! * - strict list of lazy elements
> List * ! - lazy list of strict elements
> List ! ! - strict list of strict elements

So what is KindInfer.constrain for, then?