October 2018 - ghc-steering-committee

Bundling patterns with type synonyms (#28)
by Christopher Allen 27 Jan '19

27 Jan '19

The proposal I'm reviewing is: Bundling patterns with type synonyms by Bertram Felgenhauer and Joe Hermaszewski https://github.com/ghc-proposals/ghc-proposals/pull/28 Having reviewed the proposal and gone through some of the GHC Trac history, I think we should accept this proposal. There are a couple of open questions, ambiguities, and potential downsides but the overall complexity of the proposal doesn't cause me great concern. Cheers, Chris Allen

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Please review #175: Lift.liftTyped, Shepherd: Ben Gamari
by Joachim Breitner 06 Nov '18

06 Nov '18

Dear Committee, this is your secretary speaking: Add `liftTyped` to the `Lift` typeclass, by Alec Theriault, was proposed https://github.com/ghc-proposals/ghc-proposals/pull/175 https://github.com/harpocrates/ghc-proposals/blob/lift-typed/proposals/0000… I propose Ben as the shepherd. Please reach consensus as described in https://github.com/ghc-proposals/ghc-proposals#committee-process I suggest you make a recommendation, in a new e-mail thread with the proposal number in the subject, about the decision, maybe point out debatable points, and assume that anyone who stays quiet agrees with you. Thanks, Joachim -- Joachim Breitner mail(a)joachim-breitner.de http://www.joachim-breitner.de/

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Discussion: List instances for a type in GHCi #166
by Iavor Diatchki 05 Nov '18

05 Nov '18

Hello, I'd like to start the discussion about feature request #166, "List instances for a type in GHCi". In short, the idea is that we add a new command to GHCi, `:instances TYPE`, which given a type, will show the list of instances---for any class---that could be used with this type. It seems like this could be a potentially handy thing to do, and it doesn't really interfere with anything else, so I recommend that we accept it. Please let me know what you think. -Iavor

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Proposal #170: Unrestricted OverloadedLabels (was: Uppercase OverloadedLabels), rec: accept
by Vitaly Bragilevsky 05 Nov '18

05 Nov '18

Hi all, The proposal #170: Unrestricted OverloadedLabels (was: Uppercase OverloadedLabels) (https://github.com/ghc-proposals/ghc-proposals/pull/170) was updated to allow any nonempty alphanumeric string following a # under OverloadedLabels. So I repeat my recommendation to accept it. Please speak up within a week if you have any concerns. Silence is understood as agreement. Regards, Vitaly

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Proposal #173: The dot type operator, rec: accept
by Eric Seidel 05 Nov '18

05 Nov '18

Hello, This proposal would extend the parser to allow the '.' character to appear in type operators, allowing one to write code like the following: ``` type (f . g) x = f (g x) foo :: (Maybe . Either Int) Bool foo = Just (Right True) ``` I recommend we accept the proposal, as it would resolve an odd inconsistency between the term and type languages. The main downside seems to be that combining a type-level '.' with a 'forall' is a bit hard to read, but I think the benefits of a more consistent syntax outweigh this concern. Eric

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Proposal #168: fail with OverloadedStrings, rec: accept
by Joachim Breitner 21 Oct '18

21 Oct '18

Dear committee, welcome back from ICFP! Those who missed it: it was great, watch the videos, come to Berlin next year. Shayne Fletcher proposed that in the presence of both RebindableSyntax and OverloadedStrings, the implicit calls to fail produces by the compiler should wrap the arguments in `fromString`: https://github.com/shayne-fletcher-da/ghc-proposals/blob/fail-rebindable-wi… I’ll shepherd that myself. I agree with Neil Mitchell in the assessment that this feels more like a bug fix than a proposal, and support acceptance. Cheers, Joachim -- Joachim Breitner mail(a)joachim-breitner.de http://www.joachim-breitner.de/

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Proposal #174: Lower precedence for {-# UNPACK #-}, rec: accept
by Joachim Breitner 21 Oct '18

21 Oct '18

Dear committee, Vladislav proposed that we lower precedence for {-# UNPACK #-}: https://github.com/int-index/ghc-proposals/blob/unpack-pragma-precedence/pr… I’ll shepherd that myself. Simon already nodded, it’s half implemented and a clear win. Happy to recommend acceptance. Cheers, Joachim -- Joachim Breitner mail(a)joachim-breitner.de http://www.joachim-breitner.de/

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Linear types (#111): conditional acceptance
by Richard Eisenberg 19 Oct '18

19 Oct '18

Hi all, Several members of the steering committee met at ICFP to discuss the Linear Types proposal, #111. While some concerns were raised about the utility of the proposed approach (as also explained on the GitHub trail), the committee agreed that the best way forward would be to accept the proposal. I thus propose *conditional acceptance*, subject to these conditions, which were discussed at ICFP: 1. Error messages must remain free of mention of linear types, unless -XLinearTypes is in effect (or some flag like -fprint-linear-types is on). The same must be true of using the `:type` facility in GHCi. 2. Type inference must remain backward-compatible. All programs accepted today must be accepted when -XLinearTypes is not in effect. Ideally, these programs would also be accepted when -XLinearTypes is in effect, but there can be some wiggle room here. 3. Compile times for programs without -XLinearTypes must not unduly increase. Anything approaching or over a 2% across-the-board increase in compile times would be a cause for concern. 4. There must be no degradation in runtime performance of GHC-compiled programs. Linear types in Core might, for example, make some optimizations harder to apply; however, we must find a way to get runtime performance on par with what we have today. 5. There must be a story for a migration of `base`. The committee is concerned that, once linear types hits, there will be a great demand to incorporate linear types into `base`. (Note that `fmap` may want a linear type, and due to Functor's status as a superclass of Monad, `fmap` is really baked in.) How will this work? In particular, how will Haddock render newly-linearized types? 6. The theory of the linear types must be sound. This seems to be the case today, but as things evolve, we want to state explicitly that this must remain true. In particular, we must be able to rely on the safety of using linear mutable arrays. 7. There must be a specification (in some typeset document) of the new core language, written out for public inspection. If the final version of this should violate these prescriptions, it does not immediately mean we are at an impasse -- it just means that we need to have more discussion. Before officially posting this on #111 on behalf of the committee, I'd like some feedback on this recommendation. As usual, I'll take silence for agreement. Discussion period: 1 week (shortened due to the fact that many have already participated in formulating this list) Thanks! Richard

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Please Review: Show Types as Symbols (#164), Shepherd: Richard Eisenberg
by Joachim Breitner 17 Oct '18

17 Oct '18

Dear Committee, this is your secretary speaking: Provide a primitive to show types as Symbols, by Sandy Maguirer, was proposed https://github.com/ghc-proposals/ghc-proposals/pull/164 I propose Richard as the shepherd, he already showed interest in this proposal. Please reach consensus as described in https://github.com/ghc-proposals/ghc-proposals#committee-process I suggest you make a recommendation, in a new e-mail thread with the proposal number in the subject, about the decision, maybe point out debatable points, and assume that anyone who stays quiet agrees with you. Thanks, Joachim -- Joachim Breitner mail(a)joachim-breitner.de http://www.joachim-breitner.de/

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Please review #166: List instances for a type in GHCi, Shepherd: Iavor
by Joachim Breitner 11 Oct '18

11 Oct '18

Dear Committee, this is your secretary speaking: List instances for a type in GHCi, by Xavier Denis, was proposed https://github.com/ghc-proposals/ghc-proposals/pull/166 I propose Iavor as the shepherd. Please reach consensus as described in https://github.com/ghc-proposals/ghc-proposals#committee-process I suggest you make a recommendation, in a new e-mail thread with the proposal number in the subject, about the decision, maybe point out debatable points, and assume that anyone who stays quiet agrees with you. Thanks, Joachim -- Joachim Breitner mail(a)joachim-breitner.de http://www.joachim-breitner.de/

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