On 15/12/2022 16:49, Chris Dornan wrote:
Does anybody object to us accepting #270 now? Speak now, etc.
I object to accepting #270 as-is, I'm afraid.
I'm content to accept the parts relating to -Wpuns/-Wpun-bindings, which seem to be relatively well-motivated and specified in the proposal (albeit primarily by the medium of examples). Indeed they form the bulk of the proposal content!
However the parts related to extensions seem problematic and have given rise to substantial discussion:
* We don't yet have a clear consensus on the approach to language extensions (as is being discussed elsewhere), which makes it difficult to reach agreement on whether the proposal should be modifying existing extensions or introducing new ones.
* In particular, if we modify ExplicitNamespaces it will become more problematic to introduce it as part of GHC2023, which leaves
https://github.com/ghc-proposals/ghc-proposals/issues/551 unresolved.
* ExplicitNamespaces is under-specified at present, which is not the proposer's fault, but by modifying it we will make it yet more complex and inconsistent (e.g. allowing either "type" or "data" at the top level, but only "type" in the impspec unless PatternSynonyms is enabled).
* I disagree with Simon's "The proposal is quite clear about the delta to ExplicitNameSpaces." For example, it doesn't specify or provide any examples of imports with an impspec; does "import M type (T(MkT))" silently import T but not MkT, or it it an error?
* The change to PatternSynonyms and introducing of -Wpattern-namespace-qualifier is not clearly motivated in the text (though one can imagine some motivations), and we should consider whether breaking old code in this way is justified.
I'm sure these issues can be resolved, but I think the best way to do so is to accept the -Wpuns/-Wpun-bindings parts of the proposal, while asking for the changes to extensions to be raised as a separate proposal with its own motivation, specification and examples. (This isn't about "formatting", so if splitting the proposal seems problematic it would also be fine for the whole proposal to be resubmitted; but that seems like it will be harder than a split.)
I would point out the guidelines in our README:
> If the technical debate is not rapidly resolved, the shepherd should
> return the proposal for revision. Further technical discussion can
> then take place, the author can incorporate that conclusions in the
> proposal itself, and re-submit it. Returning a proposal for revision
> is not a negative judgement; on the contrary it might connote "we
> absolutely love this proposal but we want it to be clear on these
> points".
>
> In fact, this should happen if any substantive technical debate takes
> place. The goal of the committee review is to say yes/no to a proposal
> as it stands.
With apologies for causing controversy,
Adam
On 15 Dec 2022, at 08:14, Simon Peyton Jones <simon.peytonjones@gmail.com <mailto:simon.peytonjones@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@chrisdornan.com <mailto:chris@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@richarde.dev
<mailto:lists@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@chrisdornan.com <mailto:chris@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@gmail.com
<mailto:simon.peytonjones@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@chrisdornan.com <mailto:chris@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@well-typed.com <mailto:adam@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@well-typed.com <mailto:adam@well-typed.com>
<mailto:adam@well-typed.com <mailto:adam@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@well-typed.com <mailto:adam@well-typed.com>
<mailto:adam@well-typed.com <mailto:adam@well-typed.com>>
<mailto:adam@well-typed.com <mailto:adam@well-typed.com>
<mailto:adam@well-typed.com <mailto:adam@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/Registered in England & Wales, OC335890
27 Old Gloucester Street, London WC1N 3AX, England
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