[ghc-steering-committee] #682: Explicit Level Imports, recommendation: accept
Malte Ott
malte.ott at maralorn.de
Fri Feb 7 12:16:26 UTC 2025
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/
> _______________________________________________
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