Re: [ghc-steering-committee] #668: Allow reserved identifiers as fields in OverloadedRecordDot, recommendation: accept

My preference is A>B>C>D Though my preference between A and B is weak. Whatever's easier really. On Thu, 20 Mar 2025 at 19:04, Simon Marlow via ghc-steering-committee < ghc-steering-committee@haskell.org> wrote:

I don't feel all that strongly except that C seems like a bad idea. A = B

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D > C

Cheers Simon

On Wed, 19 Mar 2025 at 21:49, Adam Gundry via ghc-steering-committee < ghc-steering-committee@haskell.org> wrote:

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Hi everyone,

This proposal [0] has been lingering for quite some time, unfortunately. So we can make progress, I've tried to summarise our options below; please vote for your preferred option in the next week or two. Once we have decided on our preferred course of action, I'll make any necessary editorial changes to the proposal.

To recap, the idea is to extend OverloadedRecordDot such that it permits record selection expressions such as

foo.type -> getField @"type" foo

even though `type` is a keyword and hence not a valid record field in a traditional datatype declarations. This is primarily motivated by the use of OverloadedRecordDot in libraries such as `persistent` (see [1]), which will generate instances like this:

instance HasField "type" SomeRecord SomeField1 where getField = ...

instance HasField "bar" SomeRecord SomeField2 where getField = ...

Both these instances are accepted, so it is quite surprising and annoying that `foo.type` is a syntax error, even though `foo.bar` will be accepted (and turn into a call to `getField @"bar"`).

As a small syntactic change, the proposal has lead to quite some discussion and a few plausible alternatives:

A. Accept the proposal as it stands, since it is the smallest change that resolves the issue.

B. Extend the proposal to permit still wider syntax, e.g. `foo.Uppercase` or `foo."quoted string"`, motivated by consistency with OverloadedLabels and use cases such as [2]. This seems reasonable to me.

C. Extend the proposal to permit keywords such as `type` to be used as field names in traditional record syntax, e.g. `data Foo = Foo { type :: Int }`. In my view this is unnecessary complexity that mistakenly conflates OverloadedRecordDot with traditional record syntax; the motivation for keywords as selector names comes from uses of OverloadedRecordDot that do not involve traditional record syntax.

D. Reject the proposal entirely, e.g. due to worries about syntax highlighting.

Please reply with your preference order amongst these options. My vote is B > A > C > D.

Thanks,

Adam

[0] https://github.com/ghc-proposals/ghc-proposals/pull/668

[1]

https://github.com/ghc-proposals/ghc-proposals/pull/668#issuecomment-2561282...

[2]

https://github.com/ghc-proposals/ghc-proposals/pull/668#issuecomment-2564274...

On 05/11/2024 13:58, Arnaud Spiwack wrote:

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I have no opinion on this. But I've seen two points in the thread which make sense: Vlad, our guardian of the parser, says that it's a good idea, and the comparison with OverloadedLabel (made by Vlad and others) is apt, and the symmetry is desirable. Ideally the comparison with OverloadedLabel should be made in the Alternatives section, but I don't feel like insisting about it :) .

On Sat, 2 Nov 2024 at 21:21, Simon Peyton Jones mailto:simon.peytonjones@gmail.com> wrote:

I'm in support too, but I have made some substantive suggestions on the GitHub ticket that I'd like to see addressed before we tie a bow on this.

Simon

On Sat, 2 Nov 2024 at 09:25, Sebastian Graf mailto:sgraf1337@gmail.com> wrote:

I'm in support as well, but would like to see a single clarifying sentence added to the proposal.

https://github.com/ghc-proposals/ghc-proposals/pull/668#discussion_r18265330... < https://github.com/ghc-proposals/ghc-proposals/pull/668#discussion_r18265330...

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Am Sa., 2. Nov. 2024 um 07:29 Uhr schrieb Erik de Castro Lopo mailto:erikd@mega-nerd.com>:

I am in support.

Erik

Matthías Páll Gissurarson wrote:

> I’m in support. No need to keep reservations longer than necessary. > > /Matti Palli > > > On Fri, Nov 1, 2024 at 23:22 Malte Ott mailto:malte.ott@maralorn.de>

wrote:

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> > > > > On 2024-10-29 20:12, Adam Gundry wrote: > > > https://github.com/ghc-proposals/ghc-proposals/pull/668 https://github.com/ghc-proposals/ghc-proposals/pull/668 > > > > I’m in support. > > > > Best > > Malte > > _______________________________________________ > > ghc-steering-committee mailing list > > ghc-steering-committee@haskell.org mailto:ghc-steering-committee@haskell.org > >

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

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> >

--

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

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and https://tweag.io https://tweag.io.

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