[ghc-steering-committee] Record dot syntax: vote results

Tue Mar 31 11:48:20 UTC 2020

What features of the proposal document are actually a part of the proposal?

Well, all of it!   I had supposed that had been clear for some time; my apologies if not.  If are other aspects of the proposal that you don’t like, please say so now!

There are two pretty much orthogonal things going on

  1.  Syntax for record selection  r.x; this proposal
  2.  Using overloading to resolve duplicate record labels, via getField/setField
It’s true (2) pretty much precludes selection/update for records with polymorphic fields (unless we have impredicativity, which I think we should ignore for now).  That has always been true.

If you don’t want (2) then (1) is still useful.   Maybe the proposal should have different desugaring rules with and without OverloadedRecordFields.   That would be an additional box in the matrix, which I suppose we might want to fill in.

Including Shayne and Neil in this conversation.

Simon

From: Richard Eisenberg <rae at richarde.dev>
Sent: 31 March 2020 12:37
To: Simon Marlow <marlowsd at gmail.com>
Cc: Simon Peyton Jones <simonpj at microsoft.com>; Neil Mitchell <ndmitchell at gmail.com>; ghc-steering-committee <ghc-steering-committee at haskell.org>; Joachim Breitner <mail at joachim-breitner.de>; Shayne Fletcher <shayne.fletcher at daml.com>
Subject: Re: [ghc-steering-committee] Record dot syntax: vote results

Quoting from the document:

> The proposal is entirely about syntax; and specifically about
  introducing the form `r.x` for record field selection.  No changes
  to the type system, or any other aspect of the language, are
  proposed.  The original proposal was more elaborate, providing ways
  to update fields as well as set them, but was simplified to focus on
  the essentials.

Is this fact enshrined in the proposal document? I view that as ground truth. And it describes, e.g., that (e { field = val }) now means (setField ...), which means that polymorphic record update is incompatible with -XRecordDotSyntax. What features of the proposal document are actually a part of the proposal?

Otherwise, I am happy with the tone and content of the post.

Thanks,
Richard

On Mar 31, 2020, at 11:40 AM, Simon Marlow <marlowsd at gmail.com<mailto:marlowsd at gmail.com>> wrote:

On Tue, 31 Mar 2020 at 11:08, Simon Peyton Jones via ghc-steering-committee <ghc-steering-committee at haskell.org<mailto:ghc-steering-committee at haskell.org>> wrote:
Thanks Joachim.

Everyone: I have extended our choices document with a draft post to the Github thread.
https://docs.google.com/document/d/1MgovHRUUNjbuM4nM8qEe308MfbAYRh2Q8PxFHl7iY74/edit?usp=sharing<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.google.com%2Fdocument%2Fd%2F1MgovHRUUNjbuM4nM8qEe308MfbAYRh2Q8PxFHl7iY74%2Fedit%3Fusp%3Dsharing&data=02%7C01%7Csimonpj%40microsoft.com%7Cd3178be33a584af741f808d7d567c97c%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637212514046325345&sdata=LeXgcQuZXFbZ8qwKu%2FmvA0PYYMAv46JlTIuYHagDJcE%3D&reserved=0>

Can you review it, for both tone and content?  You have edit permission, so by all means improve the wording.  Look for omissions.  I want to bring the discussion to a close, not re-ignite further debate, but be respectful of those who disagree.

Before we accept the proposal I think we should have a precise description of the changes to the syntax. For example, we don't address the question of whether a field name can be an operator or not. We explicitly left these questions until later; wouldn't now be the right time to address them?

Also worth bringing up at this point, since we landed on C2a: Note 5 says

One mechanism for handling this is given in the proposal<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fshayne-fletcher-da%2Fghc-proposals%2Fblob%2Frecord-dot-syntax%2Fproposals%2F0000-record-dot-syntax.md%232322-parsing-of-field-selections&data=02%7C01%7Csimonpj%40microsoft.com%7Cd3178be33a584af741f808d7d567c97c%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637212514046325345&sdata=Pcac6GXwXXCfPJt8u62ZTd1Vmq0hViqV2eRUPdYv358%3D&reserved=0>.  It involves no changes to the lexer, but instead an adjacency test one production of the parser.

I'm not sure about this as a language design. (1) it's an ad-hoc side-condition that can't be expressed in the lexical or context-free grammar (however there's precedent for this kind of thing in the form of the layout rule of course), and (2) it's quite a costly feature in terms of implementation effort to add to the language, because your AST needs complete and accurate source-span information. We can do it in GHC, and haskell-src-exts can do it nowadays, but earlier versions of haskell-src-exts before complete SrcSpanInfo was added wouldn't have been able to implement this rule. Arguably we're only accepting this as a GHC extension and not a Haskell extension in general, but as we know GHC is the testbed for future language extensions, so it's a good time to consider these issues.

The alternative of course is to go with some variant of

     *   Use the “tight infix” mechanism from this (accepted) GHC proposal<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fghc-proposals%2Fghc-proposals%2Fpull%2F229&data=02%7C01%7Csimonpj%40microsoft.com%7Cd3178be33a584af741f808d7d567c97c%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637212514046335298&sdata=r7FVNdNPqkn1N7N5NIViELWI%2F%2BjtdOjcArHCK%2BeP1oA%3D&reserved=0>

which is also an ad-hoc side-condition sadly, but could be implemented in the lexer.  Nevertheless, all this needs to be nailed down before the proposal can be accepted, IMO.

Cheers
Simon

Could you do so this week, by end Friday?   I propose to leave the votes recorded there, but when posting I'll move the post from the document (deleting it from there) to GitHub.

I'm cc'ing Neil and Shayne, the authors.  Neil, Shayne: I think (and desperately hope!) you'll be content with this outcome.  Can you review my draft post too?

Simon

|  -----Original Message-----
|  From: ghc-steering-committee <ghc-steering-committee-bounces at haskell.org<mailto:ghc-steering-committee-bounces at haskell.org>>
|  On Behalf Of Joachim Breitner
|  Sent: 30 March 2020 17:48
|  To: ghc-steering-committee <ghc-steering-committee at haskell.org<mailto:ghc-steering-committee at haskell.org>>
|  Subject: Re: [ghc-steering-committee] Record dot syntax: vote results
|
|  Dear Committe,
|
|  thanks all for voting. The ranking of votes is now
|
|        C2a > C2b > C4 > C1 > C7 > C6 > C3 > C5
|
|  In particular C2a beats every other options by 7:4 or more, and is
|  therefore the result of this poll.
|
|  You can see more statistics at
|  https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.cond
|  orcet.vote<https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Forcet.vote%2F&data=02%7C01%7Csimonpj%40microsoft.com%7Cd3178be33a584af741f808d7d567c97c%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637212514046335298&sdata=rkSKjyK%2FJA8uBNPwPVr0%2Bv6aN8pzNwRVawnY6dsvnhw%3D&reserved=0>%2FVote%2FAB23CE70AC%2F&data=02%7C01%7Csimonpj%40microsoft.c
|  om%7Ce27e9c8f455b436e2bee08d7d4ca3538%7C72f988bf86f141af91ab2d7cd011db47%7
|  C1%7C0%7C637211837260982595&sdata=LLWCxVjXxyLqcJUZ9iMgB%2B5QYGMuHFzJga
|  u9agTakiQ%3D&reserved=0
|
|  So, does this conclude this saga?
|
|  Cheers,
|  Joachim
|
|  --
|  Joachim Breitner
|    mail at joachim-breitner.de<mailto:mail at joachim-breitner.de>
|
|  https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.joach
|  im-
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