[ghc-steering-committee] Modification to record dot syntax propsal
Richard Eisenberg
rae at richarde.dev
Thu Mar 4 20:01:33 UTC 2021
I think this all comes back to: What does an extension mean? I think it means that users are opting into a language feature. For me, the existence of an extension emphatically does *not* mean that the extension is potentially part of some future standard. I think this viewpoint is different for others of us, and it's worth having a conversation about this. I may start that conversation soon, if no one beats me to it.
Under my interpretation of extension (opt-in feature), -XOverloadedRecordUpdate works great. I have never knowingly used type-changing update, though I see why it can be useful. While the fork-like nature of the proposal is regrettable, I think it's worthwhile, on balance. I was aware of this particular issue back when we were deciding about the original proposal and voted in favor of acceptance. My stance has not changed.
So, for me, it's not about "saving face", which I agree is generally a poor reason to make a poor decision. I want to keep the feature as proposed on its own merits. Indeed, I would be happy to fully advertise both new extensions (that is, -XOverloadedRecordDot and -XOverloadedRecordUpdate) in the next release of GHC. The reason I'm also happy to keep the second one less advertised is because an update is in the works, as we've been told -- not because I find the original proposal bad.
And, just to reiterate my position: if it's implemented and not statically excluded, it should be documented. For an experimental feature that is subject to change, the documentation burden is lower (but not absent). But extensions are discoverable, for example with ghc --supported-extensions. The extensions also live in GHC.LanguageExtension, so that downstream tools know of the extensions GHC supports. I have had several times when I've run across undocumented features in GHC, and it's been quite frustrating to figure out what they do. I don't think we should intentionally make this mistake. All I'm asking for is a mention in the manual, with a statement that the feature is subject to change, and with a pointer to the proposal. More is fine, too, but my minimum ask is pretty small.
Richard
> On Mar 4, 2021, at 12:59 PM, Eric Seidel <eric at seidel.io> wrote:
>
> Yes that clears up the current situation. And from the current email chain it looks like the authors are aware of the plan to send record updates back for revision? I'd just want to make sure that the updated proposal reflects that split on which parts have been accepted.
>
> For what it's worth, I do recall the loss of type-changing update being part of the original proposal and thought the proposal was still good on balance. The tradeoffs were definitely discussed in the giant Github thread, I don't recall if we discussed that aspect here though.. Regardless, I think it's a bad look for us to walk back a decision on account of not having read the proposal closely enough!
>
> On Thu, Mar 4, 2021, at 09:53, Simon Peyton Jones wrote:
>> | That being said, I don't see anything in the revised proposal about
>> | the stability of OverloadedRecordUpdate. Are you saying that as part
>> | of this revision, we'll explicitly accept OverloadedRecordDot and send
>> | OverloadedRecordUpdate back for revision?
>>
>> We *already* accepted both, as part of accepting the earlier
>> RecordDotSyntax proposal. But in this round, Iavor has pushed back
>> against OverloadedRecordUpdate. No one else has expressed a view on
>> this point.
>>
>> But rather than debate it at length I proposed to explicitly un-accept
>> the OverloadedRecordUpdate part of the proposal. It'll return as part
>> of a new record-update proposal that Adam is working on.
>>
>> In the meantime OverloadedRecordUpdate will be in GHC's codebase, and
>> (assuming that's what the majority wants) documented in the user
>> manual, with a prominent "may change" caveat.
>>
>> Does that make it clear?
>>
>> Simon
>>
>> | -----Original Message-----
>> | From: ghc-steering-committee <ghc-steering-committee-
>> | bounces at haskell.org> On Behalf Of Eric Seidel
>> | Sent: 04 March 2021 14:38
>> | To: ghc-steering-committee at haskell.org
>> | Subject: Re: [ghc-steering-committee] Modification to record dot
>> | syntax propsal
>> |
>> | I agree with Richard and Joachim that it should be documented in the
>> | user guide. It's much better to document features with the expected
>> | level of support than to let users stumble upon them and make their
>> | own assumptions about stability.
>> |
>> | That being said, I don't see anything in the revised proposal about
>> | the stability of OverloadedRecordUpdate. Are you saying that as part
>> | of this revision, we'll explicitly accept OverloadedRecordDot and send
>> | OverloadedRecordUpdate back for revision?
>> |
>> | On Thu, Mar 4, 2021, at 04:46, Simon Peyton Jones via ghc-steering-
>> | committee wrote:
>> | >
>> | > Friends
>> | >
>> | >
>> | >
>> | > We've agree to accept my suggestion below.
>> | >
>> | >
>> | >
>> | > But there is one point at issue: should OverloadedRecordUpdate be
>> | > documented in the user manual, albeit identified as a not-yet-
>> | accepted
>> | > feature?
>> | >
>> | >
>> | >
>> | > * Richard positively wants it in the manual
>> | > * Iavor positively doesn't want it there.
>> | >
>> | >
>> | > I don't mind either way.
>> | >
>> | >
>> | >
>> | > What do others think? It's not a big deal, but we owe the authors a
>> | > decision. Answer by the end of the week please, and I'll make a
>> | > shepherd decision based on the opinions I get.
>> | >
>> | >
>> | >
>> | > Simon
>> | >
>> | >
>> | >
>> | >
>> | >
>> | > *From:* Simon Peyton Jones <simonpj at microsoft.com>
>> | > *Sent:* 02 March 2021 12:45
>> | > *To:* ghc-steering-committee <ghc-steering-committee at haskell.org>
>> | > *Cc:* Simon Peyton Jones <simonpj at microsoft.com>
>> | > *Subject:* RE: [ghc-steering-committee] Modification to record dot
>> | > syntax propsal
>> | >
>> | >
>> | >
>> | > Friends
>> | >
>> | >
>> | >
>> | > Having consulted the authors, I propose that we do this:
>> | >
>> | >
>> | >
>> | > * Proceed with OverloadedRecordDot for 9.2, exactly as in the
>> | > original proposal except for the extension name.
>> | > * Record update will remain exactly as now, in 9.2; that is,
>> | drawing
>> | > back from the original proposal.
>> | > * There may be some *code* in 9.2 that allows overloaded record
>> | > update, protected by OverloadedRecordUpdate, but not in the user
>> | > manual, and not treated as an accepted proposal. I don't think we
>> | > should ask the authors to remove it, and it will allow
>> | experimentation.
>> | > * Adam is leading on a revised record-update proposal. This will
>> | cover
>> | > * the tradeoffs between type-changing and non-type-changing
>> | update
>> | > * what the current record-update syntax stands for, and/or any
>> | new
>> | > syntax
>> | >
>> | >
>> | > Is that acceptable to everyone?
>> | >
>> | >
>> | >
>> | > Simon
>> | >
>> | >
>> | >
>> | > *From:* ghc-steering-committee
>> | > <ghc-steering-committee-bounces at haskell.org> *On Behalf Of *Simon
>> | > Peyton Jones via ghc-steering-committee
>> | > *Sent:* 01 March 2021 17:51
>> | > *To:* Iavor Diatchki <iavor.diatchki at gmail.com>; Spiwack, Arnaud
>> | > <arnaud.spiwack at tweag.io>
>> | > *Cc:* ghc-steering-committee <ghc-steering-committee at haskell.org>
>> | > *Subject:* Re: [ghc-steering-committee] Modification to record dot
>> | > syntax propsal
>> | >
>> | >
>> | >
>> | > I don't buy the argument of "this is already accepted", as I don't
>> | > think many of us had noticed that part of the proposal (I certainly
>> | > didn't), and I think we should be flexible enough to revisit
>> | previous
>> | > decisions when we notice problems with them.
>> | >
>> | > I agree in principle that we can revisit decisions. But we have to
>> | be
>> | > aware that it is potentially very discouraging for proposal authors
>> | to
>> | >
>> | > * propose something,
>> | > * have it *extensively* debated (including this very point),
>> | > * have it accepted,
>> | > * implement it,
>> | > and then be told that the committee has changed its mind. That's
>> | > pretty bad from their point of view.
>> | >
>> | >
>> | >
>> | > Still, Adam is working on a new SetField proposal, so perhaps that's
>> | a
>> | > figleaf. I'll consult them.
>> | >
>> | >
>> | > Simon
>> | >
>> | >
>> | >
>> | >
>> | >
>> | > *From:* Iavor Diatchki <iavor.diatchki at gmail.com>
>> | > *Sent:* 01 March 2021 17:23
>> | > *To:* Spiwack, Arnaud <arnaud.spiwack at tweag.io>
>> | > *Cc:* Simon Peyton Jones <simonpj at microsoft.com>;
>> | > ghc-steering-committee <ghc-steering-committee at haskell.org>
>> | > *Subject:* Re: [ghc-steering-committee] Modification to record dot
>> | > syntax propsal
>> | >
>> | >
>> | >
>> | > Hello,
>> | >
>> | >
>> | >
>> | > I think there is a strong motivation to *at least* split the
>> | > extensions: with the current design, enabling the special `.`
>> | notation
>> | > also *disables* type changing record update, which has nothing to do
>> | > with the `.` notation.
>> | >
>> | >
>> | >
>> | > My preference would be to:
>> | >
>> | > 1. Split the original proposal into two parts: one about `.`
>> | > notation, the other about record update (as suggested by this
>> | proposal)
>> | >
>> | > 2. Treat the `.` notation part as accepted
>> | >
>> | > 3. Require changes on the record update part, so that you don't
>> | have
>> | > to choose between it and type changing record updates, which are
>> | quite
>> | > useful, and I don't think we should aim for a Haskell without them.
>> | >
>> | >
>> | >
>> | > I don't buy the argument of "this is already accepted", as I don't
>> | > think many of us had noticed that part of the proposal (I certainly
>> | > didn't), and I think we should be flexible enough to revisit
>> | previous
>> | > decisions when we notice problems with them.
>> | >
>> | >
>> | >
>> | > -Iavor
>> | >
>> | >
>> | >
>> | >
>> | >
>> | >
>> | >
>> | > On Mon, Mar 1, 2021 at 1:40 AM Spiwack, Arnaud
>> | <arnaud.spiwack at tweag.io> wrote:
>> | >
>> | > > Simon, all,
>> | >
>> | > >
>> | >
>> | > > After reading more of the PR thread (in particular the fews posts
>> | after Simon's recommendation), I have to admit: I am thoroughly
>> | confused. I'm not sure that two people in that thread have the same
>> | motivation, end goal, or design in mind.
>> | >
>> | > >
>> | >
>> | > > The motivations provided by the modified *Alternatives* section is
>> | not much more helpful (at the risk of caricaturing a little, it
>> | basically reads: "we made two extensions rather than one because we
>> | can"). Though it makes it clear that the end goal is to fold a bunch
>> | of record-related extensions into one glorious record extension (well,
>> | probably not fold them, but make a meta-extension that implies all the
>> | extensions that we've decided we like).
>> | >
>> | > >
>> | >
>> | > > My starting point is that:
>> | >
>> | > > - Additional extensions have a maintenance cost
>> | >
>> | > > - Additional extensions impose a cognitive burden on their use
>> | >
>> | > > - I expect that a new extension will break my code in the next few
>> | releases.
>> | >
>> | > >
>> | >
>> | > > Based on this, I don't care how this extension or the glorious
>> | record extension are named; but if we want to have two extensions we
>> | should have a serious reason. Right now, the one reason that I see
>> | (and Iavor raised), is that the update part of `RecordDotSyntax` is
>> | not backward compatible. Is it a strong enough reason? I don't know.
>> | The only data point that I can provide is that when we discussed the
>> | original proposal, I brought it up several times, and it didn't seem
>> | very important at the time (the conversation focused on other points
>> | of the proposal).
>> | >
>> | > >
>> | >
>> | > > So, I'm still reluctant. I feel that, at the very least, the
>> | motivations are not well-enough articulated in the proposal (I'll make
>> | a comment to this effect on Github when I'm done composing this
>> | email).
>> | >
>> | > >
>> | >
>> | > > I appreciate that I'm in the minority here. Yet, I'm still
>> | unconvinced.
>> | >
>> | > >
>> | >
>> | > > Best,
>> | >
>> | > > Arnaud
>> | >
>> | > >
>> | >
>> | > > On Sat, Feb 27, 2021 at 12:39 AM Simon Peyton Jones
>> | <simonpj at microsoft.com> wrote:
>> | >
>> | > >> Generally, I'm not in favour in proposals which split extensions
>> | though: we already have so many extensions. Are the reasons for this
>> | split strong enough? I haven't had time to dig into the details.
>> | >
>> | > >> Arnaud, happily, you don't have to dig very deep - just read the
>> | handful of posts following my recommendation.
>> | >
>> | > >>
>> | >
>> | > >> There seem to be two motivations.
>> | >
>> | > >>
>> | >
>> | > >> 1. There really are two orthogonal extensions, one for r.x
>> | notation, and one for overloaded update. Iavor likes the first but
>> | not the second. Neil likes both. Having separate extensions lets us
>> | experiment.
>> | > >>
>> | >
>> | > >> 1. You suggest that changing the definition of RecordDotSyntax
>> | in a subsequent release, e.g. by subsequently making it imply
>> | NoFieldSelectors, would be fine. But it certainly imposes pain - some
>> | programs would stop compiling. The approach offered by this proposal
>> | avoids that problem.
>> | > >>
>> | >
>> | > >> Yes, there are lots of extensions surrounding records:
>> | NoFieldSelectors, DuplicateRecordFields, NamedFieldPuns,
>> | DisambiguateRecordFields, RecordWildCards. It may not be pretty to
>> | divide things up so fine, but it's not new.
>> | >
>> | > >>
>> | >
>> | > >>
>> | >
>> | > >> If there are alternative suggestions, let's hear them.
>> | >
>> | > >>
>> | >
>> | > >> Simon
>> | >
>> | > >>
>> | >
>> | > >> *From:* ghc-steering-committee <ghc-steering-committee-
>> | bounces at haskell.org> *On Behalf Of *Spiwack, Arnaud
>> | > >> *Sent:* 26 February 2021 22:33
>> | > >> *To:* Iavor Diatchki <iavor.diatchki at gmail.com>
>> | > >> *Cc:* ghc-steering-committee <ghc-steering-committee at haskell.org>
>> | > >> *Subject:* Re: [ghc-steering-committee] Modification to record
>> | dot syntax propsal
>> | >
>> | > >>
>> | >
>> | > >>
>> | >
>> | > >>> I do think that reusing the record update syntax for the
>> | overloaded monomorphic update is a mistake---it is not something I had
>> | noticed during our original discussion.
>> | >
>> | > >>
>> | >
>> | > >> This is the one reason I can see for cutting this extension in
>> | smaller pieces. But, then again, -XOverloadedRecordUpdate would be a
>> | fork-like extension.
>> | >
>> | > >>
>> | >
>> | > >> Generally, I'm not in favour in proposals which split extensions
>> | though: we already have so many extensions. Are the reasons for this
>> | split strong enough? I haven't had time to dig into the details.
>> | >
>> | > >>
>> | >
>> | > >> I'm not sure that not having the design of the proposal quite
>> | finalised is a good reason, extensions mutate in their first
>> | iterations, I don't think that it's a problem.
>> | >
>> | > _______________________________________________
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>> | > ghc-steering-committee at haskell.org
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