[ghc-steering-committee] Modifiers and #512: NoFieldSelectors

[Adam Gundry]

It's certainly unfortunate that this proposal has been stalled for so long.

I think there is rough consensus that modifiers-style syntax would be 
preferable to the pragma syntax suggested in the proposal. That's 
slightly different from requiring Modifiers in its full glory to be 
implemented prior to this proposal, because one could implement the 
proposal more directly (e.g. having the parser recognise 
%NoFieldSelectors just as it could recognise {-# NoFieldSelectors #-}). 
Thus we don't need a synchronisation point: if necessary the amended 
NoFieldSelectors proposal can be implemented first and then the 
Modifiers implementation can generalise it.

So I'd suggest we "conditionally accept" the proposal, on the basis that 
it is amended to use modifier syntax, giving a clear signal to the 
author that the proposal isn't going to get stuck again. By 
"conditionally accept" I mean we wouldn't insist on another full round 
of committee review once the revisions are made.

Also, given the delays, I think it would be best if one of us offers to 
take care of the work of revising the proposal, rather than requiring 
the author to do it (but of course asking their opinion on this proposed 
approach).

Does this sound reasonable? Some of this may be what Vlad means by 
"Revise the proposal to use modifiers-based syntax and then accept", I'm 
not sure.

Cheers,

Adam


On 18/12/2023 08:59, Arnaud Spiwack wrote:
> Here's my thought.
> 
> If the modifiers implementation arrives before #512 is implemented, then 
> it's fair to amend the proposal. If the modifiers implementation arrives 
> after #512 is implemented, then it will be time to amend the proposal, 
> add the modifier version of #512, and deprecate the pragma. If there 
> hasn't been a release of the pragma version, then it can be deleted 
> entirely. I don't really feel there needs to be additional 
> synchronisation points imposed onto contributors.
> 
> On Thu, 14 Dec 2023 at 13:35, Richard Eisenberg <rae at richarde.dev 
> <mailto:rae at richarde.dev>> wrote:
> 
>     Concur. Let's boldly go into the future with modifiers. :)
> 
>     Thanks, Vlad.
> 
>     Richard
> 
>>     On Dec 11, 2023, at 4:31 PM, Simon Peyton Jones
>>     <simon.peytonjones at gmail.com <mailto:simon.peytonjones at gmail.com>>
>>     wrote:
>>
>>         If we choose to revise, I volunteer to implement Modifiers in
>>         time for GHC 9.12 
>>
>>
>>     Like Joachim, this changes the situation a lot.  Thank you for
>>     offering.  You are an excellent implementor, and if you say you'll
>>     do it, I'm sure you will.  Don't forget that, to be useful for the
>>     author, the modifiers need to be in Template-Haskell-generated
>>     syntax too.
>>
>>     With that in mind:
>>
>>     * [ x] Revise the proposal to use modifiers-based syntax and then
>>     accept
>>
>>     I'm sure the author will be happy to use modifier syntax -- he
>>     just needs to be sure that doing so won't block the feature and
>>     your offer gives him that surety.
>>
>>     Simon
>>
>>     On Mon, 11 Dec 2023 at 12:40, Vladislav Zavialov
>>     <vlad.z.4096 at gmail.com <mailto:vlad.z.4096 at gmail.com>> wrote:
>>
>>         Dear Committee Members,
>>
>>         Our previous discussion regarding #512 was inconclusive.
>>
>>         Thread 1:
>>         https://mail.haskell.org/pipermail/ghc-steering-committee/2022-November/002991.html <https://mail.haskell.org/pipermail/ghc-steering-committee/2022-November/002991.html>
>>         Thread 2:
>>         https://mail.haskell.org/pipermail/ghc-steering-committee/2022-December/003015.html <https://mail.haskell.org/pipermail/ghc-steering-committee/2022-December/003015.html>
>>
>>         #512 is the proposal that introduces per-declaration,
>>         per-constructor, and per-field NoFieldSelectors annotations.
>>
>>         I'm not quite sure how to summarize the discussion because
>>         everyone seems to have a unique view. But it all revolves
>>         around a syntactic issue: should the proposal use pragma-based
>>         syntax or modifiers-based syntax?
>>
>>         Here are two facts to inform your opinion:
>>
>>         1. The Modifiers proposal is accepted, and it makes sense to
>>         use it for the proposed feature
>>         2. The Modifiers proposal is, however, unimplemented
>>
>>         So at the moment #512 says that we'd first introduce the
>>         pragma-based syntax, and when Modifiers are implemented we
>>         could deprecate the pragma-based syntax in favor of Modifiers.
>>
>>         I am *strongly* opposed to introducing a feature that we know
>>         is destined for deprecation. But not everyone shares this
>>         attitude, apparently, so let's vote.
>>
>>         Here are the options. Select all that you find acceptable
>>         (multiple-choice):
>>         * [ ] Accept the proposal with pragma-based syntax, then
>>         deprecate it and switch to modifiers-based syntax
>>         * [ ] Accept the proposal with pragma-based syntax, do not
>>         switch to modifiers-based syntax
>>         * [ ] Revise the proposal to use modifiers-based syntax and
>>         then accept
>>         * [ ] Reject the proposal regardless of syntax
>>
>>         Before you vote, let me try to sway you towards the "revise"
>>         option. If we choose to revise, I volunteer to implement
>>         Modifiers in time for GHC 9.12. I believe Modifiers are a
>>         splendid idea and I envision many good uses for them.
>>
>>         Vlad


-- 
Adam Gundry, Haskell Consultant
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