Re: [ghc-steering-committee] Please review #641: Wildcard binders in type declarations

As per my earlier email, I have very little opinion about that, and I'm happy to follow Simon's recommendation. On Fri, 19 Apr 2024 at 13:28, Matthías Páll Gissurarson wrote:

I don’t seem to have write access to that sheet, but I’ve requested it now.

I was on the fence here, and would have voted to park it until it was requested. But as int-index points out, a breaking change to TH is on the way anyway, and it would be good to improve the completeness at the same time.

So I vote accept (mildly)

/Matti Palli

On Fri, Apr 19, 2024 at 12:45 Vladislav Zavialov wrote:

...

I don't think I have a vote, as my term has ended. Even if I had one, I'd abstain because it is my amendment.

However, I'd like to point out two things.

1. If the proposed amendment is rejected, we /still/ have to change template-haskell to implement 425 in its current form. The specification allows invisible wildcards `@_`, which can't be represented in template-haskell at the moment. So I'd like to ask voting members to take that into consideration: this is not an "unforced change" because there is a change coming either way.

2. Simon argues against a new recursive data type in the AST. OK, I can see the problem, but please don't forget about non-recursive forms `type T _ = rhs` and `type T (_ :: k) = rhs`. Even if there is no user demand for nested forms like `type T ((_ :: k1) :: k2) = rhs`, flat wildcard binders are a less intrusive addition and I've personally wanted them several times. So if the problem is recursion, please consider sending the amendment for revision instead of rejecting it.

Thus the voting options should probably be:

a) accept the amendment b) revise the amendment to avoid recursive/nested forms c) reject the amendment

Vlad

On Fri, Apr 19, 2024 at 12:15 PM Simon Peyton Jones < simon.peytonjones@gmail.com> wrote:

...

Dear GHC Steering Committee

On 2 April I asked:

I think it's time to vote. Please so before Monday morning *[8 April]*.

...

Thank you!

*It is now 19 April, of the eight members of the committee only Malte has voted. *

Please please vote. Today! Use email and record your vote on the spreadsheet https://docs.google.com/spreadsheets/d/1e6GdwHmAjeDEUhTvP-b18MDkpTfH3SMHhFu5.... Vlad you have a vote; since you are the proposer you may choose to abstain but I think it's up to you.

The proposal isn't a huge deal either way, but we owe it to the proposer and to ourselves to deal with our business in a timely way.

Simon

On Tue, 2 Apr 2024 at 17:25, Simon Peyton Jones < simon.peytonjones@gmail.com> wrote:

...

Dear GHC Steering Committee

Vlad proposes to amend proposal #425 https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0425-de...to permit more wildcard binder forms in type declarations: https://github.com/ghc-proposals/ghc-proposals/pull/641

See my mail below. I recommend, fairly strongly, to park this until there is evidence of need.

- it's an unforced change, - with no user demand - but some real user impact (notably: it will break some TH users) - and some implementation cost (modest but very non-zero) - aiming to anticipate as-yet-unknown future requirements -- but YAGNI https://martinfowler.com/bliki/Yagni.html

I think it's time to vote. Please so before Monday morning. Thank you!

Simon

On Thu, 21 Mar 2024 at 09:56, Simon Peyton Jones < simon.peytonjones@gmail.com> wrote:

...

Dear Steering Committee

Vlad proposes to amend proposal #425 https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0425-de...to permit more wildcard binder forms in type declarations: https://github.com/ghc-proposals/ghc-proposals/pull/641

You may find it easiest to look at the rich diff https://github.com/ghc-proposals/ghc-proposals/pull/641/files?short_path=cb2... .

This is a pretty small generalisation which would allow

data T (( (a :: k1) :: k2)) = ...

in which the binder has multiple kind signatures and redundant parens. The change is *not driven by user need*, but rather solely by *uniformity*: these same forms are permitted in function definitions:

f :: forall (a :: k). blah f @(((a::k1)::k2))) = ...

is permitted.

It imposes a change on Template Haskell syntax too.

The implementation becomes a bit more complicated; more recursive data types, etc. Nothing hard, but more.

It's not a big deal either way. Very few people expressed a view on GitHub. My personal view is that the modest (albeit non-zero) gain does not justify the definite (albeit modest) pain. I would leave this until someone actually wants it.

Vlad argues for future-proofing, but my experience is that an eye to the future is sensible when you are making changes anyway; but making unforced changes solely for the future risks incurring pain now that, when the future comes, turns out to have been a poor investment. We may have correctly anticipated, or we may not.

So my recommendation is to park this until we get a real user demand.

It's a perfectly sensible proposal, but adopting it is a judgement call. I'll leave a week for committee responses, and then we can just vote.

Simon

On Thu, 21 Mar 2024 at 08:07, Adam Gundry wrote:

...

Dear Committee,

Vlad proposes to amend proposal #425 to permit more wildcard binder forms in type declarations:

https://github.com/ghc-proposals/ghc-proposals/pull/641

I'd like to nominate Simon PJ as the shepherd.

Please guide us to a conclusion as outlined in https://github.com/ghc-proposals/ghc-proposals#committee-process

Cheers,

Adam

-- Adam Gundry, Haskell Consultant Well-Typed LLP, https://www.well-typed.com/

Registered in England & Wales, OC335890 27 Old Gloucester Street, London WC1N 3AX, England https://www.google.com/maps/search/27+Old+Gloucester+Street,+London+WC1N+3AX,+England?entry=gmail&source=g _______________________________________________ ghc-steering-committee mailing list ghc-steering-committee@haskell.org

https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee

_______________________________________________ ghc-steering-committee mailing list ghc-steering-committee@haskell.org https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee

_______________________________________________ ghc-steering-committee mailing list ghc-steering-committee@haskell.org https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee

_______________________________________________ ghc-steering-committee mailing list ghc-steering-committee@haskell.org https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee

-- Arnaud Spiwack Director, Research at https://moduscreate.com and https://tweag.io.