[ghc-steering-committee] Recommendation for #378: support the design for dependent types

Thu May 13 15:09:07 UTC 2021

Friends
You have now had a month to review my recommendation below, to accept #378: support for dependent types. Here it is once more<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fgoldfirere%2Fghc-proposals%2Fblob%2Fdependent-types%2Fproposals%2F0000-dependent-type-design.rst&data=04%7C01%7Csimonpj%40microsoft.com%7Cc0e29b49960a43b4d7ee08d8fff24512%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637540763362468484%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=K1JBnklN2ztnUyibLJ%2Bv9q8%2BK%2Bg1Sf%2FHDGjwVmj25Mw%3D&reserved=0>
I have heard

  *   Support: Joachim, Vitaly, Alejandro, Vlad (plus Richard and myself)
  *   Against: no one
But that leaves Tom, Eric, Arnaud, Cale, Simon M, and Iavor who have not expressed an opinion.  Please do!
Failing further feedback, I'll accept on Tuesday next week.
There has been some further discussion on the pull request<https://github.com/ghc-proposals/ghc-proposals/pull/378>, but I don't think any fundamentally new points have come up.  This is clearly a judgement call, but one I think we should make.  Haskell has always been a research lab - that's part of what makes it distinctive.  I think we can continue to celebrate that innovation.  But see my email immediately below for what we are and are not accepting.
Simon

From: Simon Peyton Jones <simonpj at microsoft.com>
Sent: 15 April 2021 10:39
To: ghc-steering-committee at haskell.org
Cc: Simon Peyton Jones <simonpj at microsoft.com>
Subject: Recommendation for #378: support the design for dependent types

Dear GHC steering committee
OK Richard has now revised the "Design for Dependent Types" proposal, and has resubmitted it.  As we asked, it now includes the design sketch that constitutes the direction of travel advocated in the proposal, rather than merely referring to it.
Here it is once more<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fgoldfirere%2Fghc-proposals%2Fblob%2Fdependent-types%2Fproposals%2F0000-dependent-type-design.rst&data=04%7C01%7Csimonpj%40microsoft.com%7Cc0e29b49960a43b4d7ee08d8fff24512%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637540763362468484%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=K1JBnklN2ztnUyibLJ%2Bv9q8%2BK%2Bg1Sf%2FHDGjwVmj25Mw%3D&reserved=0>
I propose acceptance.
Remember:

  *   We would not be accepting every detail of the design in Section 4 - rather, we expect further specific proposals as we move in the direction described in the proposal.   So we should not debate the fine print of Section 4.
  *   We would be accepting that the proposal describes a direction of travel that we are happy with.  That in turn gives people the confidence to invest efforts in those more detailed proposals.  As the "Proposed change specification" says:  "When evaluating new proposals, the GHC committee would consider compatibility with the design sketch below. Generally speaking, new proposals should be forward-compatible with the design sketch; that is, the new features proposed would continue to be at home when surrounded by other dependent-type features."
Any views?   Questions of clarification or technical questions belong on the comment stream.
Thanks
Simon
From: ghc-steering-committee <ghc-steering-committee-bounces at haskell.org<mailto:ghc-steering-committee-bounces at haskell.org>> On Behalf Of Simon Peyton Jones via ghc-steering-committee
Sent: 06 April 2021 13:58
To: ghc-steering-committee at haskell.org<mailto:ghc-steering-committee at haskell.org>
Subject: Re: [ghc-steering-committee] Recommendation for #378: support the design for dependent types

Richard and I have discussed this.
We concluded that we'd put it back into "Needs revision" status. He's going to expand it (substantially) to include the proposed design sketch of dependent types on the GHC wiki<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2F-%2Fwikis%2Fdependent-haskell&data=04%7C01%7Csimonpj%40microsoft.com%7Cc0e29b49960a43b4d7ee08d8fff24512%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637540763362478476%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=C5Ywef9f5MK4jEc2XfmXeZ26YIdJeP0%2F%2BKfGdIhfkYA%3D&reserved=0>.  Then he'll resubmit in the hope of getting approval of the design in principle, subject to subsequent discussion of the fine detail.
Simon

From: Simon Peyton Jones <simonpj at microsoft.com<mailto:simonpj at microsoft.com>>
Sent: 29 March 2021 13:17
To: ghc-steering-committee at haskell.org<mailto:ghc-steering-committee at haskell.org>
Cc: Simon Peyton Jones <simonpj at microsoft.com<mailto:simonpj at microsoft.com>>
Subject: Recommendation for #378: support the design for dependent types

Dear GHC Steering Committee
I'm recommending acceptance of Proposal #378: Support the design for dependent types<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fghc-proposals%2Fghc-proposals%2Fpull%2F378&data=04%7C01%7Csimonpj%40microsoft.com%7Cc0e29b49960a43b4d7ee08d8fff24512%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637540763362478476%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=%2Bf32VqzdL6HgiF436%2FGWPwBl09c1qo%2BAMbgPY6tJfSI%3D&reserved=0>
As you'll see, there is a lot of useful context, but the payload is pretty simple

When evaluating new proposals, the GHC committee would consider compatibility with the proposed design sketch of dependent types on the GHC wiki<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2F-%2Fwikis%2Fdependent-haskell&data=04%7C01%7Csimonpj%40microsoft.com%7Cc0e29b49960a43b4d7ee08d8fff24512%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637540763362488470%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=1xOofIrHU3rP91mxYwvKnefFqCA5RBHCUUuKHqtdZlo%3D&reserved=0>. Generally speaking, new proposals should be forward-compatible with the design sketch; that is, the new features proposed would continue to be at home when surrounded by other dependent-type features.

Of course, the committee remains free to revise the design sketch or to accept proposals that encroach upon it (i.e. contradicting this guidance), but such choices should be made explicitly.

See also the committee's Review Criteria<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fghc-proposals%2Fghc-proposals%2F%23review-criteria&data=04%7C01%7Csimonpj%40microsoft.com%7Cc0e29b49960a43b4d7ee08d8fff24512%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637540763362488470%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=C%2B6VLghDD03q1Qwqwytrp75eAHQtPF%2FB1SveNIKrymA%3D&reserved=0>: put another way, this proposal says that we consider the design sketch alongside other features of today's Haskell when assessing a new proposal's fit with the language.

Note that compatibility with dependent types is far from the only criterion the committee would use to evaluate a proposal. Other review criteria, such as learnability, clarity of error messages, performance, etc., remain just as ever.
Any views?  Let's try to converge rapidly.... the proposal has been substantially refined by a lot of debate.
Simon
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