[ghc-steering-committee] Please review #518: Type vs Constraint proposal, Shepherd: Eric

[Simon Peyton Jones]

Eric

Would it be possible to conclude this discussion now?  And (I earnestly
hope) accept the proposal?  I don't think it's controversial, and it barely
needs a proposal anyway (since it's mainly about GHC internals).

I thought I'd start work on implementing it, in case that threw up any
issues.  I got drawn in, and have not invested about two person weeks in
the MR.  So I'm keen to get this done.  Thanks!

Simon

On Wed, 13 Jul 2022 at 01:51, Eric Seidel <eric at seidel.io> wrote:

> Hi all,
>
> Richard and Simon PJ have proposed tightening up the distinction between
> Type and Constraint in the type system. This proposal is primarily
> motivated by eliminating a long-standing class of compiler bugs, but it
> introduces a number of new (user-facing) types at the core of GHC's type
> system. And it does bring with it some additional capabilities like unboxed
> and unlifted implicit parameters, and a greater ability to abstract over
> arrows.
>
> I recommend acceptance of the proposal, but there is one question that I
> would like the broader committee to engage on.
>
> Simon and Richard have proposed introducing another arrow type as part of
> this proposal.
>
> type (==>) :: forall (r1 :: RuntimeRep) (r2 :: RuntimeRep).
>               CONSTRAINT r1 -> CONSTRAINT r2 -> Constraint
>
> I am a bit wary of introducing this arrow as a stable API at this point.
> It does not seem strictly necessary to make this part of the public API to
> implement this proposal, but doing so would commit us to a particular point
> in the design space. I've started a thread to discuss this on GitHub,
> please take a look and chime in if you have thoughts.
>
>
> https://github.com/ghc-proposals/ghc-proposals/pull/518#discussion_r917416818
>
> Thanks!
> Eric
>
> On Wed, Jul 6, 2022, at 08:10, Joachim Breitner wrote:
> > Dear Committee,
> >
> > The Type vs Constraint proposal
> > has been submitted by Richard Eisenberg and Simon Peyton Jones
> >
> > https://github.com/ghc-proposals/ghc-proposals/pull/518
> >
> https://github.com/ghc-proposals/ghc-proposals/blob/spj/type-vs-constraint/proposals/0000-type-vs-constraint.rst
> >
> > I suggest that Eric shepherds this proposal.
> >
> > Please guide us to a conclusion as outlined in
> > https://github.com/ghc-proposals/ghc-proposals#committee-process
> >
> > Thanks,
> > Joachim
> >
> >
> >
> >
> >
> > --
> > Joachim Breitner
> >   mail at joachim-breitner.de
> >   http://www.joachim-breitner.de/
> >
> > _______________________________________________
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