<div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Sorry for the late reply!<br><br>After reading the thread, I'm slightly in favor of having 2 extensions.<br><br>While I agree that we already have too many extensions, the case for having two extensions is convincing. As Arnaud mentioned, extensions are often used in a long list in the .cabal file, and being able to have ExplicitLevelImports enabled during refactoring seems to be a win. We want to keep migration costs minimal.<br><br>The subtle case of the list of extensions being order-dependent (as Richard mentioned) is a bit troubling, but I agree that that should be left to another proposal.<br></div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Thu, 6 Feb 2025 at 08:26, Arnaud Spiwack <<a href="mailto:arnaud.spiwack@tweag.io">arnaud.spiwack@tweag.io</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>Simon M: I'm pretty we would enable either both or neither in editions, yes.</div><div><br></div><div>---</div><div><br></div><div>Erik: See the argument summarized by Simon PJ here <a href="https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomment-2609199731" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomment-2609199731</a> , and the handful of comment below, these are the arguments which have been laid down so far for either side of this conversation. My summary of the summary is that there are two envisioned use-case for turning on ExplicitLevelImports while leaving ImplicitStagePersistence on:</div><div><br></div><div>- Migration (this help compile a project, but progressively follow warnings to prepare a project for NoImplicitStagePersistence)<br></div>- Exceptional ImplicitStagePersistence: in the current state of the library, it seems that you will sometimes need to use ImplicitStagePersistence (to define Lift function, perhaps, or in a module where you define a bunch of Template Haskell: not every problem has been solved). But because you are in a project which uses ExplicitLevelImport everywhere, you may want to still mark your imports consistently with the rest of the project, as being imports for slices, quotes, or neither.<br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, 6 Feb 2025 at 00:37, Simon Marlow <<a href="mailto:marlowsd@gmail.com" target="_blank">marlowsd@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>I don't feel strongly about 1 vs 2 extensions, because I think the direction of travel is away from recommending individual extensions as a way to interact with the compiler and towards GHC20xx instead. And in GHC20xx I think we would enable either both or neither of these extensions, correct?</div><div><br></div><div>Cheers</div><div>Simon<br></div><br><div><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, 5 Feb 2025 at 08:16, Erik de Castro Lopo <<a href="mailto:erikd@mega-nerd.com" target="_blank">erikd@mega-nerd.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi,<br>
<br>
I have read through the proposal, but there is something I am still unsure<br>
of. For the LANGUAGE pragma's is there any utility in using one separately<br>
form the other? It seems there isn't. In any one file you would use either<br>
one or the other.<br>
<br>
Thanks,<br>
Erik<br>
<br>
Arnaud Spiwack wrote:<br>
<br>
> Sorry I disappeared for a while. I second Simon's call, let's vote. Let me<br>
> repost a link to Simon's pro and cons post<br>
> <a href="https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomment-2609199731" rel="noreferrer" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomment-2609199731</a><br>
> <br>
> So far, we have the following votes<br>
> <br>
> - Simon: 1 extension<br>
> - Adam: 2 extension (feels quite strongly about it)<br>
> - Sebastian: 1 extension (on the Github thread, but I'll count it as a vote<br>
> anyway)<br>
> <br>
> Eric, Moritz, Malta, Matthías, Erik, Jakob: what do you think?<br>
> <br>
> ---<br>
> <br>
> Beyond that we have a single piece of community feedback on the Github<br>
> thread. It's from Michael Peyton Jones who is in favour of 2 extensions,<br>
> find it here<br>
> <a href="https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomment-2609583126" rel="noreferrer" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomment-2609583126</a><br>
> <br>
> ---<br>
> <br>
> For the record, I hadn't commented about it in my recommendation, despite<br>
> my well-known and desperately public distaste for micro extensions. I have<br>
> a couple of reasons:<br>
> - I dislike micro-extensions less now that we are doing the GHC20XX (the<br>
> last one was very modest, I'm in favour, by the way, of doing a much more<br>
> ambitious language edition soon, otherwise my distaste will come back with<br>
> a vengeance)<br>
> - While I consider every proposal with several extensions in it with<br>
> suspicion, the authors did argue for their second extension, I found the<br>
> argument mildly convincing, and thought it wasn't worth fighting against.<br>
> <br>
> Now, even like this my preference is mildly for one extension. Adam says<br>
> that it's easier to implement warnings with both the new syntax on and<br>
> implicit stage persistence left turned on, than to implement errors when<br>
> implicit stage persistence is turned off. It may be so, but I don't think<br>
> we can avoid implementing the errors anyway, so I don't feel that it's a<br>
> particularly compelling argument. I don't feel strongly. But that's<br>
> presumably where my vote goes.<br>
> <br>
> On Tue, 4 Feb 2025 at 07:13, Simon Peyton Jones <<a href="mailto:simon.peytonjones@gmail.com" target="_blank">simon.peytonjones@gmail.com</a>><br>
> wrote:<br>
> <br>
> > Yes: all members of the steering committee, please vote. Evaluating<br>
> > proposals is what we all signed up to do!<br>
> ><br>
> > Thanks<br>
> ><br>
> > Simon<br>
> ><br>
> > On Mon, 3 Feb 2025 at 20:45, Adam Gundry <<a href="mailto:adam@well-typed.com" target="_blank">adam@well-typed.com</a>> wrote:<br>
> ><br>
> >> I'm (unsurprisingly) in favour of acceptance, and I vote for two<br>
> >> extensions. As I commented on the GitHub thread:<br>
> >><br>
> >> > We shouldn't unnecessarily conflate a syntactic extension<br>
> >> (ExplicitLevelImports) with a semantic one (NoImplicitStagePersistence)<br>
> >> just because the common case is to want both and we want to keep the<br>
> >> number of extensions lower.<br>
> >><br>
> >> If there are reasons why having two extensions is actually problematic,<br>
> >> I'd like to hear them.<br>
> >><br>
> >> Also, at the risk of opening another avenue of discussion, we also need<br>
> >> to resolve the syntax question (see<br>
> >><br>
> >> <a href="https://github.com/ghc-proposals/ghc-proposals/pull/682#discussion_r1849123243" rel="noreferrer" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/682#discussion_r1849123243</a>).<br>
> >><br>
> >> I don't have a very strong opinion here, but given that some people do,<br>
> >> perhaps we should make ImportQualifiedPost affect splice imports so we<br>
> >> have<br>
> >><br>
> >> import splice qualified A -- By default<br>
> >> import A splice qualified -- Under ImportQualifiedPost<br>
> >><br>
> >> In any case, please do vote! It would be good to get this proposal done.<br>
> >><br>
> >> Cheers,<br>
> >><br>
> >> Adam<br>
> >><br>
> >><br>
> >><br>
> >> On 27/01/2025 11:52, Simon Peyton Jones wrote:<br>
> >> > Arnaud<br>
> >> ><br>
> >> > OK, following my call and some further iteration, the proposal is much<br>
> >> > improved. See here<br>
> >> > <<a href="https://github.com/ghc-proposals/ghc-proposals/pull/682" rel="noreferrer" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/682</a>>. Please<br>
> >> read<br>
> >> > the new "Proposed Change Specification" which has had a large rewrite.<br>
> >> ><br>
> >> > I vote to accept.<br>
> >> ><br>
> >> > BUT there is one point that the committee must resolve: *one extension<br>
> >> > of two?* It's just a judgement call and I lay out the choices in this<br>
> >> > post<br>
> >> > <<br>
> >> <a href="https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomment-2609199731" rel="noreferrer" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/682#issuecomment-2609199731</a>>.<br>
> >> I doubt that we'll get much community feedback. I suggest that we just<br>
> >> vote. I vote for one, not two. As does Sebastian.<br>
> >> ><br>
> >> > Over to you Arnaud. Let's get this one done. Matthew is busy<br>
> >> > implementing it for a customer and it has been on our to-do list for<br>
> >> > some time now. (Partly my fault.)<br>
> >> ><br>
> >> > Simon<br>
> >> ><br>
> >> > On Tue, 21 Jan 2025 at 10:48, Simon Peyton Jones<br>
> >> > <<a href="mailto:simon.peytonjones@gmail.com" target="_blank">simon.peytonjones@gmail.com</a> <mailto:<a href="mailto:simon.peytonjones@gmail.com" target="_blank">simon.peytonjones@gmail.com</a>>><br>
> >> wrote:<br>
> >> ><br>
> >> > Matthew and I had a good conversation. Some notes here<br>
> >> > <<br>
> >> <a href="https://docs.google.com/document/d/1dEMPIHpbN19xYZymGCxO0BpQR58RPhk5MslruY7yXD0/edit?usp=sharing" rel="noreferrer" target="_blank">https://docs.google.com/document/d/1dEMPIHpbN19xYZymGCxO0BpQR58RPhk5MslruY7yXD0/edit?usp=sharing</a><br>
> >> >.<br>
> >> ><br>
> >> > He's going to work on a revision to the proposal which I'll iterate<br>
> >> > with him.<br>
> >> ><br>
> >> > Simon<br>
> >> ><br>
> >> > On Tue, 21 Jan 2025 at 07:37, Arnaud Spiwack<br>
> >> > <<a href="mailto:arnaud.spiwack@tweag.io" target="_blank">arnaud.spiwack@tweag.io</a> <mailto:<a href="mailto:arnaud.spiwack@tweag.io" target="_blank">arnaud.spiwack@tweag.io</a>>> wrote:<br>
> >> ><br>
> >> > Then, let's wait until your call with Matthew and decide how to<br>
> >> > act then.<br>
> >> ><br>
> >> > On Tue, 21 Jan 2025 at 02:43, Simon Peyton Jones<br>
> >> > <<a href="mailto:simon.peytonjones@gmail.com" target="_blank">simon.peytonjones@gmail.com</a><br>
> >> > <mailto:<a href="mailto:simon.peytonjones@gmail.com" target="_blank">simon.peytonjones@gmail.com</a>>> wrote:<br>
> >> ><br>
> >> > Arnaud<br>
> >> ><br>
> >> > I have responded with a lot of feedback on the Github thread<br>
> >> > <<br>
> >> <a href="https://github.com/ghc-proposals/ghc-proposals/pull/682#pullrequestreview-2562175116" rel="noreferrer" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/682#pullrequestreview-2562175116</a><br>
> >> >.<br>
> >> ><br>
> >> > TL:DR: I like the direction of travel but have too many<br>
> >> > questions of detail to be ready to accept it just yet.<br>
> >> ><br>
> >> > I have arranged a call with Matthew.<br>
> >> ><br>
> >> > Simon<br>
> >> ><br>
> >> > On Thu, 9 Jan 2025 at 06:31, Arnaud Spiwack<br>
> >> > <<a href="mailto:arnaud.spiwack@tweag.io" target="_blank">arnaud.spiwack@tweag.io</a> <mailto:<a href="mailto:arnaud.spiwack@tweag.io" target="_blank">arnaud.spiwack@tweag.io</a>>><br>
> >> > wrote:<br>
> >> ><br>
> >> ><br>
> >> > Mathew Pickering, Rodrigo Mesquita, and our own Adam<br>
> >> > Gundry put forward a new proposal for the perenial<br>
> >> > problem of dependencies and Template Haskell<br>
> >> > <a href="https://github.com/ghc-proposals/ghc-proposals/pull/682" rel="noreferrer" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/682</a><br>
> >> > <<br>
> >> <a href="https://github.com/ghc-proposals/ghc-proposals/pull/682" rel="noreferrer" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/682</a>><br>
> >> ><br>
> >> > I've got to be honest, I'm not fully convinced by the<br>
> >> > proposal. More on that in a minute, but it learns a<br>
> >> > lesson from previous attempts at the same problem by<br>
> >> > solving the absolute minimal problem, but this leads to<br>
> >> > a somewhat fork-like situation for which it isn't clear<br>
> >> > whether it will be resolved in the future. That being<br>
> >> > said, it solves a real problem which has plagued GHC<br>
> >> > compilation forever. And I'm inclined to believe that we<br>
> >> > can't really do much better.<br>
> >> ><br>
> >> > But I'm getting ahead of myself. The problem is that<br>
> >> > when you have -XTemplateHaskell in a file, all the<br>
> >> > dependencies' compiled code must suddenly be available<br>
> >> > for typechecking. This breaks `-fno-code` and wounds<br>
> >> > recompilation avoidance. This is probably the main<br>
> >> > reason why it's a widely held belief that Template<br>
> >> > Haskell is slow: you use Template Haskell in a few<br>
> >> > modules, and suddenly your IDE is much less responsive<br>
> >> > and you recompile more files. Yay?<br>
> >> ><br>
> >> > Anyway, the general gist of the solution is clear: we<br>
> >> > must be able to specify that we don't want to import a<br>
> >> > module for Template Haskell (there is subtleties in this<br>
> >> > too as you will want a little more control than that for<br>
> >> > cross-compilation reasons which I'm not competent about<br>
> >> > to comment on). But the devil is in the many details.<br>
> >> > There's this thing called implicit cross-stage<br>
> >> > persistence which says that anything you import<br>
> >> > not-for-template-haskell is going to be available in<br>
> >> > quotes and splices anyway. Sigh… So you have to turn<br>
> >> > this off. This is what the proposal does. And pretty<br>
> >> > much only.<br>
> >> ><br>
> >> > They introduce a new<br>
> >> > extension-XNoImplicitStagePersistence which disables<br>
> >> > that, and a little bit of syntax to specify the stage of<br>
> >> > imports. That's it.<br>
> >> ><br>
> >> > But it comes with severe limitations, most importantly:<br>
> >> > you can't ever use a symbol defined in the current<br>
> >> > module in a quote or splice of this current module,<br>
> >> > typed template Haskell is turned off.<br>
> >> ><br>
> >> > For these situations, the proposal kind of advertises<br>
> >> > using `-XImplicitStagePersistence`. Which does seem like<br>
> >> > a fork-like situation to me. Not cool. Yet… yet Template<br>
> >> > Haskell is a big messy ball of yarn, and I don't think<br>
> >> > it's fair to ask of any proposal to entangle it<br>
> >> > completely. The failure of past attempts seem to support<br>
> >> > this case. And I believe the authors are correct when<br>
> >> > they claim that this proposal, in practice, covers a<br>
> >> > vast majority of the uses of Template Haskell out there.<br>
> >> > So maybe we can see that as a new foundation for<br>
> >> > Template Haskell. I'm not thrilled about it, but it's<br>
> >> > probably the most reasonable way forward.<br>
> >> ><br>
> >> > The real problem with this sort of proposal is that then<br>
> >> > I get to write way too long an email to the committee.<br>
> >> > Hopefully this didn't deter you. Read the proposal, and<br>
> >> > let's vote.<br>
> >> ><br>
> >> > --<br>
> >> > Arnaud Spiwack<br>
> >> > Director, Research at <a href="https://moduscreate.com" rel="noreferrer" target="_blank">https://moduscreate.com</a><br>
> >> > <<a href="https://moduscreate.com" rel="noreferrer" target="_blank">https://moduscreate.com</a>> and <a href="https://tweag.io" rel="noreferrer" target="_blank">https://tweag.io</a><br>
> >> > <<a href="https://tweag.io" rel="noreferrer" target="_blank">https://tweag.io</a>>.<br>
> >><br>
> >><br>
> >> --<br>
> >> Adam Gundry, Haskell Consultant<br>
> >> Well-Typed LLP, <a href="https://www.well-typed.com/" rel="noreferrer" target="_blank">https://www.well-typed.com/</a><br>
> >><br>
> >> Registered in England & Wales, OC335890<br>
> >> 27 Old Gloucester Street, London WC1N 3AX, England<br>
> >><br>
> >> _______________________________________________<br>
> >> ghc-steering-committee mailing list<br>
> >> <a href="mailto:ghc-steering-committee@haskell.org" target="_blank">ghc-steering-committee@haskell.org</a><br>
> >> <a href="https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee" rel="noreferrer" target="_blank">https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee</a><br>
> >><br>
> > _______________________________________________<br>
> > ghc-steering-committee mailing list<br>
> > <a href="mailto:ghc-steering-committee@haskell.org" target="_blank">ghc-steering-committee@haskell.org</a><br>
> > <a href="https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee" rel="noreferrer" target="_blank">https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee</a><br>
> ><br>
> <br>
> <br>
> -- <br>
> Arnaud Spiwack<br>
> Director, Research at <a href="https://moduscreate.com" rel="noreferrer" target="_blank">https://moduscreate.com</a> and <a href="https://tweag.io" rel="noreferrer" target="_blank">https://tweag.io</a>.<br>
<br>
<br>
-- <br>
----------------------------------------------------------------------<br>
Erik de Castro Lopo<br>
<a href="http://www.mega-nerd.com/" rel="noreferrer" target="_blank">http://www.mega-nerd.com/</a><br>
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</blockquote></div></div></div>
</blockquote></div><div><br clear="all"></div><br><span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature"><div dir="ltr">Arnaud Spiwack<br>Director, Research at <a href="https://moduscreate.com" rel="noopener noreferrer" target="_blank">https://moduscreate.com</a> and <a href="https://tweag.io" rel="noopener noreferrer" target="_blank">https://tweag.io</a>.</div></div>
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</blockquote></div><div><br clear="all"></div><div><br></div><span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature"><div dir="ltr"><span style="font-family:arial,helvetica,sans-serif;font-size:small">-- </span><a href="http://mpg.is/" style="font-family:arial,helvetica,sans-serif;font-size:small" target="_blank">Matthías Páll Gissurarson</a><br></div></div>