[ghc-steering-committee] Modification to record dot syntax propsal

[Simon Peyton Jones]

In terms of actual official GHC Steering Committee business, this proposal is really just about changing the name of the extension from -XRecordDotSyntax to -XOverloadedRecordDot. The implementation will simply fall short of the entire proposal. Is that accurate?

Not quite.

  *   It replaces RecordDotSyntax with two separate extensions, OverloadedRecordDot and OverloadedRecordUpdate.
  *   The second, OverloadedRecordUpdate would be advertised as experimental and subject to change. (I'm totally happy with having it in the user manual if that's what everyone is happy with.)
  *   If you switch on experimental OverloadedRecordUpdate, you get the whole proposal, with no falling short. But the committee has expressed some second thoughts about update, hence advertising it as experimental.
OK?  Only Richard, Iavor, Joachim, Arnaud have said anything on this thread.   I'm taking silence as assent ... yell by the end of today if you are unhappy.  I'd like to communicate with the authors.

Simon

From: Richard Eisenberg <rae at richarde.dev>
Sent: 02 March 2021 16:46
To: Simon Peyton Jones <simonpj at microsoft.com>
Cc: ghc-steering-committee <ghc-steering-committee at haskell.org>
Subject: Re: [ghc-steering-committee] Modification to record dot syntax propsal

I don't love having a feature that's completely unmentioned in the manual -- too much of a root to trip over. (For example, tooling may run into -XOverloadedRecordUpdate, but now has no official place to look to see what it is.) I'd be fine with a short section in the manual describing that an experimental -XOverloadedRecordUpdate extension exists, is subject to change, and is meant to roughly implement some part of some proposal. This can be done in just a few sentences, with a link to the proposal, but just being silent seems unhelpful to users.

With that small tweak, I'm quite happy to agree with the proposal here.

In terms of actual official GHC Steering Committee business, this proposal is really just about changing the name of the extension from -XRecordDotSyntax to -XOverloadedRecordDot. The implementation will simply fall short of the entire proposal. Is that accurate?

Richard


On Mar 2, 2021, at 7:45 AM, Simon Peyton Jones via ghc-steering-committee <ghc-steering-committee at haskell.org<mailto:ghc-steering-committee at haskell.org>> wrote:

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<mailto: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<mailto:iavor.diatchki at gmail.com>>; Spiwack, Arnaud <arnaud.spiwack at tweag.io<mailto:arnaud.spiwack at tweag.io>>
Cc: ghc-steering-committee <ghc-steering-committee at haskell.org<mailto: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<mailto:iavor.diatchki at gmail.com>>
Sent: 01 March 2021 17:23
To: Spiwack, Arnaud <arnaud.spiwack at tweag.io<mailto:arnaud.spiwack at tweag.io>>
Cc: Simon Peyton Jones <simonpj at microsoft.com<mailto:simonpj at microsoft.com>>; ghc-steering-committee <ghc-steering-committee at haskell.org<mailto: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<mailto: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<mailto: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<mailto: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<mailto:iavor.diatchki at gmail.com>>
Cc: ghc-steering-committee <ghc-steering-committee at haskell.org<mailto: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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