[ghc-steering-committee] #682: Explicit Level Imports, recommendation: accept
Arnaud Spiwack
arnaud.spiwack at tweag.io
Mon Feb 10 06:25:44 UTC 2025
For the record, the syntactic alternatives can be found in [§8.5 Syntactic
alternatives](
https://github.com/well-typed/ghc-proposals/blob/wip/level-imports-2024/proposals/0000-splice-imports.rst#syntactic-alternatives
)
Malte seems to be uncomfortable with the fact that the proposed syntax is
import slice Foo
import quote Bar
Even when ImportQualifiedPost, which enables the syntax
import Foo qualified [as …]
is enabled.
The proposal offers alternative syntaxes like
import Foo slice
Import Bar quote
or (to sound more English)
import Foo for slice
import Bar for quote
Richard Eisenberg, in the thread, suggests that the motivation for
ImportQualifiedPost doesn't apply to slice/quote because he believes that
there's going to be one block of import slice, one block of import
(nothing), one block of import quote, and they aren't going to be mixed
together. Them being more visually distinguished by starting with the
keyword is an asset in this view. Many seem convinced
My understanding of Malte's point is that this is not intuitive enough that
it can be left implicit in the proposal, and he'd like the proposal to at
least state explicitly that it ignores ImportQualifiedPost.
Malte, let me know if I misrepresent your point of view (or anybody else's).
On Sat, 8 Feb 2025 at 01:19, Simon Peyton Jones <simon.peytonjones at gmail.com>
wrote:
> I don’t think we were finished
> with bikeshedding the syntax. At least I think the proposal should state
> what
> the syntax is when ImportQualifiedPost is enabled and voiced that on the
> GitHub
> thread.
>
>
> OK -- but I suspect that most of us have lost context.
>
> Would you like to post (on the Github) a message explaining:
>
> - what the syntactic alternatives are
> - what you recommend
>
> That will help to focus the discussion
>
> Thanks!
>
> Simon
>
>
> On Fri, 7 Feb 2025 at 12:16, Malte Ott <malte.ott at maralorn.de> wrote:
>
>> I do not object to accepting the proposal, but I don’t think we were
>> finished
>> with bikeshedding the syntax. At least I think the proposal should state
>> what
>> the syntax is when ImportQualifiedPost is enabled and voiced that on the
>> GitHub
>> thread.
>>
>> I know we all dread wasting our time with syntax discussions but lets at
>> least
>> think about it for 5 minutes.
>>
>> Best,
>> Malte
>>
>> On 2025-02-07 15:48, Arnaud Spiwack wrote:
>> > Ok, we have enough of a quorum at this point. If everybody else
>> voted 1
>> > extension this would come at a rough draw. It can't be a strong
>> enough
>> > push to overrule the preference of the authors.
>> >
>> > I'll give it a handful more day, say until next Wednesday 12th
>> > February. If someone has a strong objection, please voice it very
>> > loudly. Otherwise I'll declare the proposal as accepted in its
>> current
>> > state.
>> >
>> > Best,
>> > Arnaud
>> >
>> > On Fri, 7 Feb 2025 at 08:01, Erik de Castro Lopo
>> > <[1]erikd at mega-nerd.com> wrote:
>> >
>> > OK, slightly in favor of two extensions.
>> >
>> > Erik
>> >
>> > Erik de Castro Lopo wrote:
>> >
>> > > Hi,
>> > >
>> > > I have read through the proposal, but there is something I am
>> > still unsure
>> > > of. For the LANGUAGE pragma's is there any utility in using one
>> > separately
>> > > form the other? It seems there isn't. In any one file you would
>> > use either
>> > > one or the other.
>> > >
>> > > Thanks,
>> > > Erik
>> > >
>> > > Arnaud Spiwack wrote:
>> > >
>> > > > Sorry I disappeared for a while. I second Simon's call, let's
>> > vote. Let me
>> > > > repost a link to Simon's pro and cons post
>> > > >
>> > [2]
>> https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomm
>> > ent-2609199731
>> > > >
>> > > > So far, we have the following votes
>> > > >
>> > > > - Simon: 1 extension
>> > > > - Adam: 2 extension (feels quite strongly about it)
>> > > > - Sebastian: 1 extension (on the Github thread, but I'll count
>> > it as a vote
>> > > > anyway)
>> > > >
>> > > > Eric, Moritz, Malta, Matthías, Erik, Jakob: what do you think?
>> > > >
>> > > > ---
>> > > >
>> > > > Beyond that we have a single piece of community feedback on the
>> > Github
>> > > > thread. It's from Michael Peyton Jones who is in favour of 2
>> > extensions,
>> > > > find it here
>> > > >
>> > [3]
>> https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomm
>> > ent-2609583126
>> > > >
>> > > > ---
>> > > >
>> > > > For the record, I hadn't commented about it in my
>> > recommendation, despite
>> > > > my well-known and desperately public distaste for micro
>> > extensions. I have
>> > > > a couple of reasons:
>> > > > - I dislike micro-extensions less now that we are doing the
>> > GHC20XX (the
>> > > > last one was very modest, I'm in favour, by the way, of doing a
>> > much more
>> > > > ambitious language edition soon, otherwise my distaste will
>> come
>> > back with
>> > > > a vengeance)
>> > > > - While I consider every proposal with several extensions in it
>> > with
>> > > > suspicion, the authors did argue for their second extension, I
>> > found the
>> > > > argument mildly convincing, and thought it wasn't worth
>> fighting
>> > against.
>> > > >
>> > > > Now, even like this my preference is mildly for one extension.
>> > Adam says
>> > > > that it's easier to implement warnings with both the new syntax
>> > on and
>> > > > implicit stage persistence left turned on, than to implement
>> > errors when
>> > > > implicit stage persistence is turned off. It may be so, but I
>> > don't think
>> > > > we can avoid implementing the errors anyway, so I don't feel
>> > that it's a
>> > > > particularly compelling argument. I don't feel strongly. But
>> > that's
>> > > > presumably where my vote goes.
>> > > >
>> > > > On Tue, 4 Feb 2025 at 07:13, Simon Peyton Jones
>> > <[4]simon.peytonjones at gmail.com>
>> > > > wrote:
>> > > >
>> > > > > Yes: all members of the steering committee, please vote.
>> > Evaluating
>> > > > > proposals is what we all signed up to do!
>> > > > >
>> > > > > Thanks
>> > > > >
>> > > > > Simon
>> > > > >
>> > > > > On Mon, 3 Feb 2025 at 20:45, Adam Gundry
>> > <[5]adam at well-typed.com> wrote:
>> > > > >
>> > > > >> I'm (unsurprisingly) in favour of acceptance, and I vote for
>> > two
>> > > > >> extensions. As I commented on the GitHub thread:
>> > > > >>
>> > > > >> > We shouldn't unnecessarily conflate a syntactic extension
>> > > > >> (ExplicitLevelImports) with a semantic one
>> > (NoImplicitStagePersistence)
>> > > > >> just because the common case is to want both and we want to
>> > keep the
>> > > > >> number of extensions lower.
>> > > > >>
>> > > > >> If there are reasons why having two extensions is actually
>> > problematic,
>> > > > >> I'd like to hear them.
>> > > > >>
>> > > > >> Also, at the risk of opening another avenue of discussion,
>> we
>> > also need
>> > > > >> to resolve the syntax question (see
>> > > > >>
>> > > > >>
>> > [6]
>> https://github.com/ghc-proposals/ghc-proposals/pull/682#discussio
>> > n_r1849123243).
>> > > > >>
>> > > > >> I don't have a very strong opinion here, but given that some
>> > people do,
>> > > > >> perhaps we should make ImportQualifiedPost affect splice
>> > imports so we
>> > > > >> have
>> > > > >>
>> > > > >> import splice qualified A -- By default
>> > > > >> import A splice qualified -- Under ImportQualifiedPost
>> > > > >>
>> > > > >> In any case, please do vote! It would be good to get this
>> > proposal done.
>> > > > >>
>> > > > >> Cheers,
>> > > > >>
>> > > > >> Adam
>> > > > >>
>> > > > >>
>> > > > >>
>> > > > >> On 27/01/2025 11:52, Simon Peyton Jones wrote:
>> > > > >> > Arnaud
>> > > > >> >
>> > > > >> > OK, following my call and some further iteration, the
>> > proposal is much
>> > > > >> > improved. See here
>> > > > >> >
>> > <[7]https://github.com/ghc-proposals/ghc-proposals/pull/682>.
>> > Please
>> > > > >> read
>> > > > >> > the new "Proposed Change Specification" which has had a
>> > large rewrite.
>> > > > >> >
>> > > > >> > I vote to accept.
>> > > > >> >
>> > > > >> > BUT there is one point that the committee must resolve:
>> > *one extension
>> > > > >> > of two?* It's just a judgement call and I lay out the
>> > choices in this
>> > > > >> > post
>> > > > >> > <
>> > > > >>
>> > [8]
>> https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomm
>> > ent-2609199731>.
>> > > > >> I doubt that we'll get much community feedback. I suggest
>> > that we just
>> > > > >> vote. I vote for one, not two. As does Sebastian.
>> > > > >> >
>> > > > >> > Over to you Arnaud. Let's get this one done. Matthew is
>> > busy
>> > > > >> > implementing it for a customer and it has been on our
>> to-do
>> > list for
>> > > > >> > some time now. (Partly my fault.)
>> > > > >> >
>> > > > >> > Simon
>> > > > >> >
>> > > > >> > On Tue, 21 Jan 2025 at 10:48, Simon Peyton Jones
>> > > > >> > <[9]simon.peytonjones at gmail.com
>> > <mailto:[10]simon.peytonjones at gmail.com>>
>> > > > >> wrote:
>> > > > >> >
>> > > > >> > Matthew and I had a good conversation. Some notes here
>> > > > >> > <
>> > > > >>
>> > [11]
>> https://docs.google.com/document/d/1dEMPIHpbN19xYZymGCxO0BpQR58R
>> > Phk5MslruY7yXD0/edit?usp=sharing
>> > > > >> >.
>> > > > >> >
>> > > > >> > He's going to work on a revision to the proposal which
>> > I'll iterate
>> > > > >> > with him.
>> > > > >> >
>> > > > >> > Simon
>> > > > >> >
>> > > > >> > On Tue, 21 Jan 2025 at 07:37, Arnaud Spiwack
>> > > > >> > <[12]arnaud.spiwack at tweag.io
>> > <mailto:[13]arnaud.spiwack at tweag.io>> wrote:
>> > > > >> >
>> > > > >> > Then, let's wait until your call with Matthew and
>> > decide how to
>> > > > >> > act then.
>> > > > >> >
>> > > > >> > On Tue, 21 Jan 2025 at 02:43, Simon Peyton Jones
>> > > > >> > <[14]simon.peytonjones at gmail.com
>> > > > >> > <mailto:[15]simon.peytonjones at gmail.com>> wrote:
>> > > > >> >
>> > > > >> > Arnaud
>> > > > >> >
>> > > > >> > I have responded with a lot of feedback on the
>> > Github thread
>> > > > >> > <
>> > > > >>
>> > [16]
>> https://github.com/ghc-proposals/ghc-proposals/pull/682#pullrequ
>> > estreview-2562175116
>> > > > >> >.
>> > > > >> >
>> > > > >> > TL:DR: I like the direction of travel but have
>> > too many
>> > > > >> > questions of detail to be ready to accept it
>> > just yet.
>> > > > >> >
>> > > > >> > I have arranged a call with Matthew.
>> > > > >> >
>> > > > >> > Simon
>> > > > >> >
>> > > > >> > On Thu, 9 Jan 2025 at 06:31, Arnaud Spiwack
>> > > > >> > <[17]arnaud.spiwack at tweag.io
>> > <mailto:[18]arnaud.spiwack at tweag.io>>
>> > > > >> > wrote:
>> > > > >> >
>> > > > >> >
>> > > > >> > Mathew Pickering, Rodrigo Mesquita, and
>> our
>> > own Adam
>> > > > >> > Gundry put forward a new proposal for the
>> > perenial
>> > > > >> > problem of dependencies and Template
>> > Haskell
>> > > > >> >
>> > [19]https://github.com/ghc-proposals/ghc-proposals/pull/682
>> > > > >> > <
>> > > > >> [20]https://github.com/ghc-proposals/ghc-proposals/pull/682
>> >
>> > > > >> >
>> > > > >> > I've got to be honest, I'm not fully
>> > convinced by the
>> > > > >> > proposal. More on that in a minute, but it
>> > learns a
>> > > > >> > lesson from previous attempts at the same
>> > problem by
>> > > > >> > solving the absolute minimal problem, but
>> > this leads to
>> > > > >> > a somewhat fork-like situation for which
>> it
>> > isn't clear
>> > > > >> > whether it will be resolved in the future.
>> > That being
>> > > > >> > said, it solves a real problem which has
>> > plagued GHC
>> > > > >> > compilation forever. And I'm inclined to
>> > believe that we
>> > > > >> > can't really do much better.
>> > > > >> >
>> > > > >> > But I'm getting ahead of myself. The
>> > problem is that
>> > > > >> > when you have -XTemplateHaskell in a file,
>> > all the
>> > > > >> > dependencies' compiled code must suddenly
>> > be available
>> > > > >> > for typechecking. This breaks `-fno-code`
>> > and wounds
>> > > > >> > recompilation avoidance. This is probably
>> > the main
>> > > > >> > reason why it's a widely held belief that
>> > Template
>> > > > >> > Haskell is slow: you use Template Haskell
>> > in a few
>> > > > >> > modules, and suddenly your IDE is much
>> less
>> > responsive
>> > > > >> > and you recompile more files. Yay?
>> > > > >> >
>> > > > >> > Anyway, the general gist of the solution
>> is
>> > clear: we
>> > > > >> > must be able to specify that we don't want
>> > to import a
>> > > > >> > module for Template Haskell (there is
>> > subtleties in this
>> > > > >> > too as you will want a little more control
>> > than that for
>> > > > >> > cross-compilation reasons which I'm not
>> > competent about
>> > > > >> > to comment on). But the devil is in the
>> > many details.
>> > > > >> > There's this thing called implicit
>> > cross-stage
>> > > > >> > persistence which says that anything you
>> > import
>> > > > >> > not-for-template-haskell is going to be
>> > available in
>> > > > >> > quotes and splices anyway. Sigh… So you
>> > have to turn
>> > > > >> > this off. This is what the proposal does.
>> > And pretty
>> > > > >> > much only.
>> > > > >> >
>> > > > >> > They introduce a new
>> > > > >> > extension-XNoImplicitStagePersistence
>> which
>> > disables
>> > > > >> > that, and a little bit of syntax to
>> specify
>> > the stage of
>> > > > >> > imports. That's it.
>> > > > >> >
>> > > > >> > But it comes with severe limitations, most
>> > importantly:
>> > > > >> > you can't ever use a symbol defined in the
>> > current
>> > > > >> > module in a quote or splice of this
>> current
>> > module,
>> > > > >> > typed template Haskell is turned off.
>> > > > >> >
>> > > > >> > For these situations, the proposal kind of
>> > advertises
>> > > > >> > using `-XImplicitStagePersistence`. Which
>> > does seem like
>> > > > >> > a fork-like situation to me. Not cool.
>> Yet…
>> > yet Template
>> > > > >> > Haskell is a big messy ball of yarn, and I
>> > don't think
>> > > > >> > it's fair to ask of any proposal to
>> > entangle it
>> > > > >> > completely. The failure of past attempts
>> > seem to support
>> > > > >> > this case. And I believe the authors are
>> > correct when
>> > > > >> > they claim that this proposal, in
>> practice,
>> > covers a
>> > > > >> > vast majority of the uses of Template
>> > Haskell out there.
>> > > > >> > So maybe we can see that as a new
>> > foundation for
>> > > > >> > Template Haskell. I'm not thrilled about
>> > it, but it's
>> > > > >> > probably the most reasonable way forward.
>> > > > >> >
>> > > > >> > The real problem with this sort of
>> proposal
>> > is that then
>> > > > >> > I get to write way too long an email to
>> the
>> > committee.
>> > > > >> > Hopefully this didn't deter you. Read the
>> > proposal, and
>> > > > >> > let's vote.
>> > > > >> >
>> > > > >> > --
>> > > > >> > Arnaud Spiwack
>> > > > >> > Director, Research at
>> > [21]https://moduscreate.com
>> > > > >> > <[22]https://moduscreate.com> and
>> > [23]https://tweag.io
>> > > > >> > <[24]https://tweag.io>.
>> > > > >>
>> > > > >>
>> > > > >> --
>> > > > >> Adam Gundry, Haskell Consultant
>> > > > >> Well-Typed LLP, [25]https://www.well-typed.com/
>> > > > >>
>> > > > >> Registered in England & Wales, OC335890
>> > > > >> 27 Old Gloucester Street, London WC1N 3AX, England
>> > > > >>
>> > > > >> _______________________________________________
>> > > > >> ghc-steering-committee mailing list
>> > > > >> [26]ghc-steering-committee at haskell.org
>> > > > >>
>> > [27]
>> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-c
>> > ommittee
>> > > > >>
>> > > > > _______________________________________________
>> > > > > ghc-steering-committee mailing list
>> > > > > [28]ghc-steering-committee at haskell.org
>> > > > >
>> > [29]
>> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-c
>> > ommittee
>> > > > >
>> > > >
>> > > >
>> > > > --
>> > > > Arnaud Spiwack
>> > > > Director, Research at [30]https://moduscreate.com and
>> > [31]https://tweag.io.
>> > >
>> > >
>> > > --
>> > >
>> >
>> --------------------------------------------------------------------
>> > --
>> > > Erik de Castro Lopo
>> > > [32]http://www.mega-nerd.com/
>> > >
>> >
>> > --
>> >
>> --------------------------------------------------------------------
>> > --
>> > Erik de Castro Lopo
>> > [33]http://www.mega-nerd.com/
>> > _______________________________________________
>> > ghc-steering-committee mailing list
>> > [34]ghc-steering-committee at haskell.org
>> > [35]
>> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-c
>> > ommittee
>> >
>> > --
>> >
>> > Arnaud Spiwack
>> > Director, Research at [36]https://moduscreate.com and
>> > [37]https://tweag.io.
>> >
>> > References
>> >
>> > 1. mailto:erikd at mega-nerd.com
>> > 2.
>> https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomment-2609199731
>> > 3.
>> https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomment-2609583126
>> > 4. mailto:simon.peytonjones at gmail.com
>> > 5. mailto:adam at well-typed.com
>> > 6.
>> https://github.com/ghc-proposals/ghc-proposals/pull/682#discussion_r1849123243
>> > 7. https://github.com/ghc-proposals/ghc-proposals/pull/682
>> > 8.
>> https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomment-2609199731
>> > 9. mailto:simon.peytonjones at gmail.com
>> > 10. mailto:simon.peytonjones at gmail.com
>> > 11.
>> https://docs.google.com/document/d/1dEMPIHpbN19xYZymGCxO0BpQR58RPhk5MslruY7yXD0/edit?usp=sharing
>> > 12. mailto:arnaud.spiwack at tweag.io
>> > 13. mailto:arnaud.spiwack at tweag.io
>> > 14. mailto:simon.peytonjones at gmail.com
>> > 15. mailto:simon.peytonjones at gmail.com
>> > 16.
>> https://github.com/ghc-proposals/ghc-proposals/pull/682#pullrequestreview-2562175116
>> > 17. mailto:arnaud.spiwack at tweag.io
>> > 18. mailto:arnaud.spiwack at tweag.io
>> > 19. https://github.com/ghc-proposals/ghc-proposals/pull/682
>> > 20. https://github.com/ghc-proposals/ghc-proposals/pull/682
>> > 21. https://moduscreate.com/
>> > 22. https://moduscreate.com/
>> > 23. https://tweag.io/
>> > 24. https://tweag.io/
>> > 25. https://www.well-typed.com/
>> > 26. mailto:ghc-steering-committee at haskell.org
>> > 27.
>> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee
>> > 28. mailto:ghc-steering-committee at haskell.org
>> > 29.
>> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee
>> > 30. https://moduscreate.com/
>> > 31. https://tweag.io/
>> > 32. http://www.mega-nerd.com/
>> > 33. http://www.mega-nerd.com/
>> > 34. mailto:ghc-steering-committee at haskell.org
>> > 35.
>> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee
>> > 36. https://moduscreate.com/
>> > 37. https://tweag.io/
>>
>> > _______________________________________________
>> > ghc-steering-committee mailing list
>> > ghc-steering-committee at haskell.org
>> >
>> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee
>>
>> _______________________________________________
>> ghc-steering-committee mailing list
>> ghc-steering-committee at haskell.org
>> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee
>>
> _______________________________________________
> ghc-steering-committee mailing list
> ghc-steering-committee at haskell.org
> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee
>
--
Arnaud Spiwack
Director, Research at https://moduscreate.com and https://tweag.io.
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