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

I've already spoken in favour of acceptance. But I should say that the objections that I had do not hold in the current iteration of the proposal. So I'm wholeheartedly in favour of acceptance. (In fact, this proposal is barely a user-facing change, I don't think that there is any obstacle to accepting the proposal within the week). On Sun, Sep 11, 2022 at 11:30 PM Simon Peyton Jones < simon.peytonjones@gmail.com> wrote:

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 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_r91741681...

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/p...

...

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@joachim-breitner.de http://www.joachim-breitner.de/

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