[ghc-steering-committee] Proposal #270: Support pun-free code. Recommendation: accept
Chris Dornan
chris at chrisdornan.com
Thu Dec 15 09:03:52 UTC 2022
I am so tempted to take this up — it just gets us right out of the doom loop that seems to be dogging this proposal, which I have come to think is incredibly valuable, as much for the analysis and insight the proposal has generated as for tools it proposes.
My only reservation is that I think it somewhat suboptimal to couple such diverse mechanisms as the warnings and import name spaces. However, if we do the follow up then we can recast the extension as primarily about warning and implying thew new cleaned-up namespace extension.
So the pragmatist in me says yes, let’s do it, provided the rest of the committee is OK with that.
If so I will organise the follow up — I will invite Artyom and, of course, I would love any input I can get from Adam and Richard and anyone else on the committee or elsewhere. (Getting Adam onto the committee was a major coup in my opinion — but I knew that already from elsewhere.)
In general I think it would be good if we could establish a precedent where the appointed shepherd is trusted to manage the process. Here we can see how multiple inputs into the managerial process are leading to compromises that could be compromising the technical outcome, just to escape ourselves (we hope it all work out in the end, of course). When it comes to technical matters, of course, everyone must have a veto but for organisational matters I think things will go much better if each person appointed to manage the process is left to it, unless a serious problem is seen, in which case a “have you considered this” would probably be in order.
Chris
> On 15 Dec 2022, at 08:14, Simon Peyton Jones <simon.peytonjones at gmail.com> wrote:
>
> I recommend acceptance as-is.
>
> I see no difficulty with the namespace part of the proposal. Yes, the existing namespace extension is ill specified. But this proposal does not make that situation worse (the delta is clearly specified), and it seems unfair of us to penalise this proposal because of the pre-existing situation.
>
> Of course, it would be better still to have a new, subsequent proposal that clarifies the ExplicitNameSpaceProposal. Perhaps we could invite Artyom write it, as a favour to the community. Or perhaps a member of the committee might like to.
>
> Simon
>
> On Thu, 15 Dec 2022 at 00:55, Chris Dornan <chris at chrisdornan.com <mailto:chris at chrisdornan.com>> wrote:
> For reasons I have made entirely clear I _strongly_ desire this split — are you offering to take over shepherding this proposal Richard? Because I am now totally stymied and unable to manage the process.
>
>> On 15 Dec 2022, at 00:47, Richard Eisenberg <lists at richarde.dev <mailto:lists at richarde.dev>> wrote:
>>
>> I strongly oppose requesting that the proposal be split. I agree that the two parts of the proposal can notionally be separated. But sometimes I feel that, in the face of difficult decisions, this committee has punted by requesting formatting changes of proposals. My case in point is around #448 about scoped type variables. That proposal arose out of a smattering of other proposals... but the committee deemed that the other proposals were too separate and needed to be considered as a whole. So, with some effort, I put them all in one. Then members of the committee said that the proposal was too big and to break it up! I refused, and had to hold my ground despite several requests. In the end, half was accepted, and at that point I took the other half and re-proposed it. I actually don't mind that last part -- I think partial acceptance is a reasonable action. But the formatting and reformatting is quite a bit of work, and I'm not convinced it really helped our debate. I'm worried we're repeating this here.
>>
>> Richard
>>
>>> On Dec 13, 2022, at 10:50 AM, Chris Dornan <chris at chrisdornan.com <mailto:chris at chrisdornan.com>> wrote:
>>>
>>> Although the two aspects of the proposal were motivated by the same problem they are doing completely different things. As long as it was easier to deal with them together the path of least resistance was to keep them bundled up, but it is becoming ever clearer that they are tied up in divergent organisational as well as technical concerns. The warnings are well understood and ready to go with a patch whereas, as this thread illustrates, nobody seems to properly understand what is going on with ExplicitNameSpaces; we are still confident that we can sort it all out and confident that we want to sort it all out but still there is work to be done.
>>>
>>> Added to this there is the fact that the problems with namespaces are entirely inherited from an existing extension that is poorly documented and, as we have just discovered, poorly understood. For all the reasons explained in the proposal we are likely to be leaning more heavily on ExplicitNameSpaces as we develop DH so we really need sort out what it does and get it written down. Here is the kicker — when we do sort out ExplicitNameSpaces and write it up properly we are going to want it attached to language extension dedicated to managing ExplicitNameSpaces, not an extension bundled up with some enabled warnings.
>>>
>>> I am happy to work with Artyom to get the new proposal set up etc.
>>>
>>> Chris
>>>
>>>
>>>> On 13 Dec 2022, at 09:01, Simon Peyton Jones <simon.peytonjones at gmail.com <mailto:simon.peytonjones at gmail.com>> wrote:
>>>>
>>>> I still don't get the "split in two" thing. The proposal is quite clear about the delta to ExplicitNameSpaces. The fact that the latter is not well specified isn't the current author's fault; and the delta makes sense as part of this proposal.
>>>>
>>>> I think we should accept this one, and politely ask the author if they would consider (as a favour) writing a delta to the ExplicitNameSpaces proposal (I assume there is one?) to clarify it.
>>>>
>>>> Simon
>>>>
>>>> On Mon, 12 Dec 2022 at 22:05, Chris Dornan <chris at chrisdornan.com <mailto:chris at chrisdornan.com>> wrote:
>>>> In this case, for sure, responsibility for fixing up namespace documentation should not fall on the author of this proposal. I am thinking more that they should be strongly encouraged to submit the follow-up proposal and we provide or identify whatever assistance necessary to get the job done. It will definitely get us to a better place in my view.
>>>>
>>>> It sounds like we are in strong agreement.
>>>>
>>>> Chris
>>>>
>>>>
>>>>
>>>> > On 12 Dec 2022, at 20:11, Adam Gundry <adam at well-typed.com <mailto:adam at well-typed.com>> wrote:
>>>> >
>>>> > On 12/12/2022 16:50, Chris Dornan wrote:
>>>> >> I really think we should split this proposal into two, one to deal with warnings and the other to deal with namespaces. The warnings look to me ready to go.
>>>> >> I am further thinking that we should really welcome the followup namespace proposal as an opportunity to clarify and properly document namespaces.
>>>> >> I am sorry, I was added to the proposal very late thinking it was technically sound but I am realising it is far from the case.
>>>> >> Finally, I am quite surprised at how little documentation there seems to be on ExplicitNamespaces. Should we be asking that revised documentation be propared as part of the proposal process and that the documentation be up to scratch? It seems the least we should be asking and much more important than requiring an implementation plan. This process is increasingly the only game in town when it comes to driving forward and defining Haskell and we need to make sure stuff is being written down properly.
>>>> >
>>>> > This is a bit of a tricky issue, I think. I agree that we should strive for a proper specification of ExplicitNamespaces. The current state seems to be sadly lacking, especially if we want ExplicitNamespaces to be in GHC2023. That said, there's a risk that proposal authors will be discouraged if proposing changes entails writing specifications for existing under-specified features!
>>>> >
>>>> > I wonder if anyone has attempted to extend "A Formal Specification of the Haskell 98 Module System" to more recent GHC extensions?
>>>> >
>>>> > Adam
>>>> >
>>>> >
>>>> >>> On 12 Dec 2022, at 12:21, Adam Gundry <adam at well-typed.com <mailto:adam at well-typed.com> <mailto:adam at well-typed.com <mailto:adam at well-typed.com>>> wrote:
>>>> >>>
>>>> >>> On 12/12/2022 11:39, Simon Peyton Jones wrote:
>>>> >>>> {-# LANGUAGE ExplicitNamespaces #-}
>>>> >>>> module N where
>>>> >>>> import M (T(type MkT)) -- NB "type" import of a data constructor
>>>> >>>> v = MkT -- usage at term level Crumbs. I had not realised the proposal is to allow *nested* uses of 'type' in import lists, as you show above.
>>>> >>>
>>>> >>> The nested use is already possible with ExplicitNamespaces. Currently it allows
>>>> >>>
>>>> >>> import M (T(type MkT))
>>>> >>> import M (type MkT)
>>>> >>> import M (pattern MkT)
>>>> >>>
>>>> >>> whereas the proposal extends it to add the possibility to write
>>>> >>>
>>>> >>> import M type (MkT)
>>>> >>> import M data (MkT)
>>>> >>> import M (data MkT)
>>>> >>>
>>>> >>>
>>>> >>>> In general, I don't feel the extensions to ExplicitNamespaces included
>>>> >>>> in the proposal are very clearly specified. Actually isn't the proposal pretty clear on this, namely the first bullet of proposed change spec <https://github.com/hithroc/ghc-proposals/blob/master/proposals/0000-support-pun-free-code.md#2-proposed-change-specification <https://github.com/hithroc/ghc-proposals/blob/master/proposals/0000-support-pun-free-code.md#2-proposed-change-specification> <https://github.com/hithroc/ghc-proposals/blob/master/proposals/0000-support-pun-free-code.md#2-proposed-change-specification <https://github.com/hithroc/ghc-proposals/blob/master/proposals/0000-support-pun-free-code.md#2-proposed-change-specification>>>. It only covers
>>>> >>>> import M *type *
>>>> >>>> import M *data *as MD
>>>> >>>> where I have emboldened the new bits. Nothing about the contents of import lists. Why did you think your example is covered by the proposal?
>>>> >>>
>>>> >>> I'm trying to understand what
>>>> >>>
>>>> >>> import M type (MkT)
>>>> >>>
>>>> >>> means where MkT is a data constructor (or if it raises some kind of error). This was by analogy to the existing
>>>> >>>
>>>> >>> import M (T(type MkT))
>>>> >>>
>>>> >>> which means something today, albeit not necessarily a very sensible thing (per https://gitlab.haskell.org/ghc/ghc/-/issues/22581 <https://gitlab.haskell.org/ghc/ghc/-/issues/22581> <https://gitlab.haskell.org/ghc/ghc/-/issues/22581 <https://gitlab.haskell.org/ghc/ghc/-/issues/22581>>).
>>>> >>>
>>>> >>> I don't see a clear specification of the proposed (extended) semantics of ExplicitNamespaces in the proposal, but perhaps I've missed something?
>>>> >>>
>>>> >>> Cheers,
>>>> >>>
>>>> >>> Adam
>>>> >>>
>>>> >>>
>>>> >>>> On Mon, 12 Dec 2022 at 09:15, Adam Gundry <adam at well-typed.com <mailto:adam at well-typed.com> <mailto:adam at well-typed.com <mailto:adam at well-typed.com>> <mailto:adam at well-typed.com <mailto:adam at well-typed.com> <mailto:adam at well-typed.com <mailto:adam at well-typed.com>>>> wrote:
>>>> >>>> Actually, reading https://gitlab.haskell.org/ghc/ghc/-/issues/22581 <https://gitlab.haskell.org/ghc/ghc/-/issues/22581> <https://gitlab.haskell.org/ghc/ghc/-/issues/22581 <https://gitlab.haskell.org/ghc/ghc/-/issues/22581>>
>>>> >>>> <https://gitlab.haskell.org/ghc/ghc/-/issues/22581 <https://gitlab.haskell.org/ghc/ghc/-/issues/22581> <https://gitlab.haskell.org/ghc/ghc/-/issues/22581 <https://gitlab.haskell.org/ghc/ghc/-/issues/22581>>> I
>>>> >>>> realised I'm unclear how the proposed extensions to ExplicitNamespaces
>>>> >>>> are supposed to work. The existing situation is apparently that for a
>>>> >>>> (non-punned) data constructor, it is possible to use either a
>>>> >>>> pattern or
>>>> >>>> type qualifier in an import list (presumably because DataKinds means
>>>> >>>> the
>>>> >>>> constructor is in scope at both the term and type levels), and the
>>>> >>>> imported constructor is then usable in both contexts.
>>>> >>>> For example, the following is accepted at present:
>>>> >>>> module M where
>>>> >>>> data T = MkT
>>>> >>>> {-# LANGUAGE ExplicitNamespaces #-}
>>>> >>>> module N where
>>>> >>>> import M (T(type MkT)) -- NB "type" import of a data constructor
>>>> >>>> v = MkT -- usage at term level
>>>> >>>> The present proposal says "With type specified in the import, only
>>>> >>>> identifiers belonging to the type namespace will be brought into the
>>>> >>>> scope." I'm not exactly sure how to interpret this, does it mean the
>>>> >>>> following alternative will be accepted or rejected?
>>>> >>>> module N where
>>>> >>>> import M type (MkT)
>>>> >>>> v = MkT
>>>> >>>> I'm worried we will end up with a situation where ExplicitNamespaces
>>>> >>>> does subtly different things depending on the position of the keyword.
>>>> >>>> In general, I don't feel the extensions to ExplicitNamespaces included
>>>> >>>> in the proposal are very clearly specified. Given the discussion about
>>>> >>>> exactly which parts belong to ExplicitNamespaces/PatternSynonyms versus
>>>> >>>> separate extensions, perhaps we should accept the parts relating to
>>>> >>>> -Wpuns/-Wpun-bindings, but ask for the ExplicitNamespaces changes to be
>>>> >>>> proposed separately?
>>>> >>>> Cheers,
>>>> >>>> Adam
>>>> >>>> On 09/12/2022 11:11, Adam Gundry wrote:
>>>> >>>> > I'm broadly in favour of accepting the proposal. I realise the
>>>> >>>> history
>>>> >>>> > is complex here, so I don't think we should ask anyone to rewrite
>>>> >>>> things
>>>> >>>> > further, though in general it would be nicer to have separate
>>>> >>>> proposals
>>>> >>>> > for -Wpuns/-Wpun-bindings (which is unambiguously fine) and for the
>>>> >>>> > changes to imports (which as Joachim points out raise issues).
>>>> >>>> >
>>>> >>>> > I'm a bit concerned that the proposal does not motivate or specify
>>>> >>>> > -Wpattern-namespace-qualified very well.
>>>> >>>> >
>>>> >>>> >
>>>> >>>> > On 08/12/2022 08:33, Joachim Breitner wrote:
>>>> >>>> >> ...
>>>> >>>> >>
>>>> >>>> >> This gives us (at least) these options:
>>>> >>>> >>
>>>> >>>> >> 1. Leave ExplicitNamespaces alone, add ExplicitNamespaces to
>>>> >>>> GHC2023,
>>>> >>>> >> introduce one or two new extensions for the newer changes.
>>>> >>>> >> 2. Extend ExplicitNamespaces, and don’t add it already to GHC2023,
>>>> >>>> >> disregarding issue #551.
>>>> >>>> >> 3. Add ExplicitNamespaces to GHC2023, and still add it to GHC2023,
>>>> >>>> >> arguing that GHC20xx allows more liberal (backward-compatibile)
>>>> >>>> >> changes than, say, Haskell2010 would allow.
>>>> >>>> >>
>>>> >>>> >> Certainly 1 is the least bold move. I am not sure what the best way
>>>> >>>> >> forwards is, and welcome other opinions.
>>>> >>>> >
>>>> >>>> > I would prefer a variant of 1: allow "data" as a keyword in
>>>> >>>> import lists
>>>> >>>> > under ExplicitNamespaces, but make the other changes under other
>>>> >>>> > extensions.
>>>> >>>> >
>>>> >>>> > As I've said previously, I have a general preference for multiple
>>>> >>>> small,
>>>> >>>> > orthogonal extensions rather than changing existing extensions to
>>>> >>>> add
>>>> >>>> > unrelated features that happen to be in similar territory. I realise
>>>> >>>> > this is controversial, of course.
>>>> >>>> >
>>>> >>>> > Cheers,
>>>> >>>> >
>>>> >>>> > Adam
>>>> >
>>>> >
>>>> > --
>>>> > Adam Gundry, Haskell Consultant
>>>> > Well-Typed LLP, https://www.well-typed.com/ <https://www.well-typed.com/>
>>>> >
>>>> > Registered in England & Wales, OC335890
>>>> > 27 Old Gloucester Street, London WC1N 3AX, England
>>>> >
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>>>>
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