[ghc-steering-committee] #370: Syntax for Modifiers, Recommendation: Acceptance

Tue Dec 15 20:06:51 UTC 2020

 It seems that everything is solve now. Are the any further objections?
Otherwise I guess in a couple of days we can mark this as accepted.

Regards,
Alejandro

On 11 Dec 2020 at 22:39:39, Alejandro Serrano Mena <trupill at gmail.com>
wrote:

>
>
> On 11 Dec 2020 at 21:35:20, Richard Eisenberg <rae at richarde.dev> wrote:
>
>> Sorry -- I've lost track here a bit. What's the issue with the grammar?
>>
>
> In this comment
> https://github.com/ghc-proposals/ghc-proposals/pull/370#issuecomment-741785189
> :
>
> Syntax: the form btype [ {modifier} -> type ] seems to allow one or zero
>> modifiers but not two. Or do I misunderstand the braces? Spell it out please
>>
>
> Regards,
> Alejandro
>
>
>> I'm quite happy to label this experimental. The key aspect of the
>> proposal is just to outline a way forward with adding syntax.
>>
>> Richard
>>
>> On Dec 10, 2020, at 4:29 AM, Alejandro Serrano Mena <trupill at gmail.com>
>> wrote:
>>
>> Should we mark them as “accepted” with the following text?
>>
>> The Committee accepts this proposal as experimental. This means that the
>>> Committee expects changes to this feature in the future, maybe as the
>>> result of other accepted proposals.
>>>
>>
>> If you agree, then we can accept this proposal once a little remaining
>> issue with the grammar has been clarified.
>>
>> Regards,
>> Alejandro
>>
>>
>> On 10 Dec 2020 at 09:59:02, Simon Peyton Jones <simonpj at microsoft.com>
>> wrote:
>>
>>> That was the point of my previous email: accept, and
>>> accept-as-experimental are actually one and the same.
>>>
>>> Objectively, yes.  But I think it helps users to advertise a feature as
>>> experimental.  It’s a signal to users that this feature is, well,
>>> experimental.  It is more likely to change.
>>>
>>> It’s only an indication not a clear distinction.  But I find it helpful.
>>>
>>> For me, it also reflects how I evaluate the proposal.  For a change to a
>>> well-established feature, we have a lot of experience in how people use
>>> that feature.
>>>
>>> For experimental features we don’t.  Example: defaulting for
>>> matchability for unsaturated type families.  We don’t have unsaturated type
>>> families right now, so we don’t have any code that uses them, and hence
>>> zero in-the-wild experience about matchability defaulting.  We shouldn’t
>>> spend ages arguing the toss – just trust Csongor’s judgement and give it a
>>> try, but advertising that details may change.
>>>
>>> Simon
>>>
>>>
>>> *From:* Spiwack, Arnaud <arnaud.spiwack at tweag.io>
>>> *Sent:* 10 December 2020 08:06
>>> *To:* Alejandro Serrano Mena <trupill at gmail.com>
>>> *Cc:* Richard Eisenberg <rae at richarde.dev>;
>>> ghc-steering-committee at haskell.org; Simon Peyton Jones <
>>> simonpj at microsoft.com>
>>> *Subject:* Re: [ghc-steering-committee] #370: Syntax for Modifiers,
>>> Recommendation: Acceptance
>>>
>>>
>>> That was the point of my previous email: accept, and
>>> accept-as-experimental are actually one and the same.
>>>
>>>
>>> What Simon is driving at, I think, is: depending on what the proposal is
>>> about, we want to apply more or less strict standard of acceptance (if a
>>> proposal is about fixing something in an existing feature, then we better
>>> be rather sure that it is indeed an improvement; but if it's about adding
>>> something new in an untrodden territory, then we can't really be sure, and
>>> it's worth experimenting with).
>>>
>>>
>>> On Wed, Dec 9, 2020 at 9:17 PM Alejandro Serrano Mena <trupill at gmail.com>
>>> wrote:
>>>
>>> Dear all,
>>>
>>> As the shepherd of this proposal, I’m quite confused about what the
>>> outcome should be. The ghc-proposals README states that:
>>>
>>>
>>> Acceptance of the proposal implies that the implementation will be
>>> accepted into GHC provided it is well-engineered, well-documented, and does
>>> not complicate the code-base too much.
>>>
>>>
>>>
>>> Most of the Committee seems to lean towards “this seems OK right now,
>>> but we don’t want to be locked” or “mark this as experimental”. However,
>>> there’s no such notion as “accept as experimental”. Furthermore, as it
>>> stands the proposal gives some syntax, and then asks any new extensions to
>>> use that syntax; so it cannot be completely thought as a feature by itself.
>>>
>>>
>>> Regards,
>>>
>>> Alejandro
>>>
>>> On 9 Dec 2020 at 15:59:43, Spiwack, Arnaud <arnaud.spiwack at tweag.io>
>>> wrote:
>>>
>>> It's always possible to change. I don't think accepting a proposal means
>>> (or ought to mean) that we are locked into anything. Accepting a proposal
>>> means that we won't oppose a design-related argument to a PR that
>>> implements (part or all of) an accepted proposal.
>>>
>>>
>>> I don't know how to quantify the degree of confidence that we have in
>>> the stability of a proposal. Here we are all saying: this is better than
>>> anything so far, and we rather need something like this to be a thing, but
>>> it's really a shot in the dark. And this lack of confidence will be
>>> reflected in the manual description. But even if we are confident in the
>>> stability of a proposal, it may very well happen that it changes
>>> dramatically, even soon.
>>>
>>>
>>> On Wed, Dec 9, 2020 at 2:55 PM Simon Peyton Jones via
>>> ghc-steering-committee <ghc-steering-committee at haskell.org> wrote:
>>>
>>> I’ve replied on GitHub.  Generally in favour.  But mark it as
>>> experimental… I don’t want to be locked into “we decided on this in Dec
>>> 2020 so now it’s too late”.  WE can learn from experience.
>>>
>>>
>>> Simon
>>>
>>>
>>> *From:* ghc-steering-committee <
>>> ghc-steering-committee-bounces at haskell.org> *On Behalf Of *Alejandro
>>> Serrano Mena
>>> *Sent:* 03 December 2020 20:17
>>> *To:* Richard Eisenberg <rae at richarde.dev>
>>> *Cc:* ghc-steering-committee at haskell.org
>>> *Subject:* Re: [ghc-steering-committee] #370: Syntax for Modifiers,
>>> Recommendation: Acceptance
>>>
>>>
>>> Dear Committee,
>>>
>>>
>>> Richard has requested for us to consider the new version of this
>>> proposal. As opposed to the previous version, this one is only about
>>> reserving syntax for “modifiers”, which at the beginning would be used for
>>> things like linearity or matchability of arrows.
>>>
>>>
>>> I think this is a good proposal, and one which would save us from
>>> re-considering syntax for every possible extension (and if linearity
>>> appears before the arrow and matchability after it, where would a future
>>> dimension go?). Thus I keep recommending acceptance on this new incarnation.
>>>
>>>
>>> Regards,
>>>
>>> Alejandro
>>>
>>>
>>> On 30 Nov 2020 at 20:52:26, Richard Eisenberg <rae at richarde.dev> wrote:
>>>
>>> To my surprise, I found myself leaning against. So I updated and
>>> simplified the proposal to remove Modifier. This makes modifiers a bit more
>>> magical, but more likely to actually work in practice. The type inference
>>> story previously may have been intractable.
>>>
>>>
>>> I've requested that the committee consider the updates in parallel with
>>> community feedback.
>>>
>>>
>>> Thanks,
>>>
>>> Richard
>>>
>>>
>>> On Nov 30, 2020, at 2:36 PM, Alejandro Serrano Mena <trupill at gmail.com>
>>> wrote:
>>>
>>>
>>> After some discussion in the GitHub thread, changes are going to arrive
>>> to the proposal. I think the best is to send the proposal back to the
>>> “Needs revision” state.
>>>
>>>
>>> Regards,
>>>
>>> Alejandro
>>>
>>>
>>> On 29 Nov 2020 at 23:12:44, Eric Seidel <eric at seidel.io> wrote:
>>>
>>> I left a few comments and questions on the PR itself, but I'm leaning
>>> towards rejecting the proposal in its current form as well. This doesn't
>>> (yet) feel like a generic mechanism, in particular because the only
>>> modifier that has been specified would be deeply wired into GHC itself.
>>>
>>> On Fri, Nov 27, 2020, at 04:46, Joachim Breitner wrote:
>>>
>>> Hi,
>>>
>>>
>>>
>>> Am Donnerstag, den 26.11.2020, 14:58 -0500 schrieb Alejandro Serrano
>>>
>>> Mena:
>>>
>>> > Dear all,
>>>
>>> > This proposal suggests adding syntax for a general notion of
>>>
>>> > modifiers, like the ones we’ve been talking about lately affecting
>>>
>>> > linearity or matchability of arrows. For example, if linear types and
>>>
>>> > unsaturated families are accepted as they stand, we would have `Int
>>>
>>> > #1 -> @U Bool` (or something like that), whereas with this proposal
>>>
>>> > we would have the more uniform `Int %1 %Unmatchable -> Bool`.
>>>
>>> >
>>>
>>> > Since the amount of modifiers is likely to increase in the future, I
>>>
>>> > think it’s a great idea to agree and reserve such syntax, instead of
>>>
>>> > coming up with different ways on each proposal. I thus recommend
>>>
>>> > acceptance of this proposal.
>>>
>>> >
>>>
>>> > The proposal itself:
>>>
>>> > (1) introduces syntax for modifiers in types and defines how to
>>>
>>> > type/kind check them,
>>>
>>> > (2) reserved such syntax for other uses in declarations and terms.
>>>
>>> >
>>>
>>> > I think the proposal still has its merits only with (1), even though
>>>
>>> > I lean towards accepting both parts of it.
>>>
>>>
>>>
>>> I like the idea of reserving syntax here, but parts of the proposal
>>>
>>> smell a bit like premature generalization to me. Are we confident that
>>>
>>> all annotations we eventually would like to use with this feature can
>>>
>>> be expressed as types of a kind that is an instance of Modifier? Or
>>>
>>> should we reserve the ability to have annotations that don't fit that
>>>
>>> model?
>>>
>>>
>>>
>>> Would we ever have annotation that may affect phases earlier than than
>>>
>>> typechecking? What if we want to use (%type e) and (%data e) to help
>>>
>>> with the SingleNamepace issues? Look like useful annotations to me, but
>>>
>>> I am not sure if they fit the framework proposed here.
>>>
>>>
>>>
>>> The fact that we special-case %1 supports that.
>>>
>>>
>>>
>>> The proposal explicitly has to state “No modifier polymorphism!”. But
>>>
>>> isn't that indication that using the type system to model the various
>>>
>>> modifiers might be the wrong tool?
>>>
>>>
>>>
>>> I wonder if there is a way where the %(…) on it’s own only reserve
>>>
>>> syntax, and the various uses of that syntax can be disambiguated
>>>
>>> _statically_ based on the content of ….
>>>
>>>
>>>
>>> Not great syntax, because not concise, enough, but morally I’d feel
>>>
>>> more at ease with
>>>
>>>
>>>
>>>   Int %(multiplicity Many) -> Int
>>>
>>>   Int %(multiplicity 1) -> Int
>>>
>>>   Int %(multiplicity m) -> Int
>>>
>>>
>>>
>>> where multiplicity is a modifier keyword, to express the existing
>>>
>>> features (including implicit generalization of m). Then we can extend
>>>
>>> this to
>>>
>>>
>>>
>>>   Int %oneShot -> Int
>>>
>>>
>>>
>>> and
>>>
>>>
>>>
>>>   Int %(matchability M) -> Int
>>>
>>>
>>>
>>> and maybe even
>>>
>>>
>>>
>>>   foo (%type [a]) -- where foo :: forall a -> ()
>>>
>>>
>>>
>>> which is a modifier that
>>>
>>>
>>>
>>>
>>>
>>> So at the moment, I am inclined to reject this proposal, until I am
>>>
>>> convinced that we are not painting ourselves into a “all modifiers are
>>>
>>> types of special kinds and that’s all the syntax and behaviour we ever
>>>
>>> need” corner.
>>>
>>>
>>>
>>> Minor detail: If we can annotate infix use of the (->) “type operator”,
>>>
>>> should we also be able to annotate other infix operators, i.e.
>>>
>>>
>>>
>>>   constr ::= (btype | ! atype) {modifier} conop (btype | ! atype)
>>>
>>>   infixexp ::= lexp {modifier} qop infixexp
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> Cheers,
>>>
>>> Joachim
>>>
>>>
>>>
>>>
>>>
>>> --
>>>
>>> Joachim Breitner
>>>
>>>   mail at joachim-breitner.de
>>>
>>>   http://www.joachim-breitner.de/
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>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>>
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>>
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