[ghc-steering-committee] #668: Allow reserved identifiers as fields in OverloadedRecordDot, recommendation: accept
Simon Marlow
marlowsd at gmail.com
Thu Mar 20 10:04:20 UTC 2025
I don't feel all that strongly except that C seems like a bad idea. A = B >
D > C
Cheers
Simon
On Wed, 19 Mar 2025 at 21:49, Adam Gundry via ghc-steering-committee <
ghc-steering-committee at haskell.org> wrote:
> 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-2561282397
>
> [2]
>
> https://github.com/ghc-proposals/ghc-proposals/pull/668#issuecomment-2564274901
>
>
>
> On 05/11/2024 13:58, Arnaud Spiwack wrote:
> > 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
> > <simon.peytonjones at gmail.com <mailto:simon.peytonjones at 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 <sgraf1337 at gmail.com
> > <mailto:sgraf1337 at 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_r1826533003
> <
> https://github.com/ghc-proposals/ghc-proposals/pull/668#discussion_r1826533003
> >
> >
> > Am Sa., 2. Nov. 2024 um 07:29 Uhr schrieb Erik de Castro Lopo
> > <erikd at mega-nerd.com <mailto:erikd at 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
> > <malte.ott at maralorn.de <mailto:malte.ott at maralorn.de>>
> wrote:
> > >
> > > >
> > > > 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
> > > > _______________________________________________
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> > > >
> >
> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee <
> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee>
> > > >
> >
> >
> > --
> >
> ----------------------------------------------------------------------
> > Erik de Castro Lopo
> > http://www.mega-nerd.com/ <http://www.mega-nerd.com/>
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> >
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> >
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> >
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> >
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> >
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> >
> >
> >
> > --
> > Arnaud Spiwack
> > Director, Research at https://moduscreate.com <https://moduscreate.com>
> > and https://tweag.io <https://tweag.io>.
> >
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>
> --
> Adam Gundry, Haskell Consultant
> Well-Typed LLP, https://www.well-typed.com/
>
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> 27 Old Gloucester Street, London WC1N 3AX, England
>
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