[ghc-steering-committee] #536: Type-level literals as a separate language extension

[Arnaud Spiwack]

I don't think that the non-forking principle informs completely on the
debate at hand. Even if the extensions are monotonic increases on the
current language, even if an extension will either be merged into the next
GHC20xx or scrapped, the question of splitting an extension in two still
has validity. You may say: well, what if we adopt the type-level literals
without adopting data kinds?

I must, at any rate, apologise: it's my role to get to a resolution on the
question of extension policy. This is going slow, and I've paused the
process during the recent discussion on stability (I'm currently at
capacity for committee work). We definitely can't wait until the policy has
been well-defined before we can make a decision on the proposal at hand.

I said I was unconvinced the last time around. I haven't changed opinion,
but I'm happy to revise if presented with a sufficiently strong motivation.

On Thu, 19 Oct 2023 at 09:07, Simon Marlow <marlowsd at gmail.com> wrote:

> Thanks for the helpful summary Vlad! Admittedly I hadn't grasped the nub
> of the issue until now.
>
> Regarding:
>
> Unfortunately, we don't have a general policy that would clearly tell us
>> which camp/paradigm is right.
>>
>
> I think we actually do have a policy that's relevant here, see "Does not
> create a language fork" in
> https://github.com/ghc-proposals/ghc-proposals#review-criteria
>
> This essentially says we are biased *against* the "customizable Haskell"
> position and in favour of the
> monotonically-increasing-set-of-language-features position.
>
> Cheers
> Simon
>
> On Wed, 18 Oct 2023 at 17:30, Vladislav Zavialov <vlad.z.4096 at gmail.com>
> wrote:
>
>> Dear Committee,
>>
>> Back in March I initiated a discussion of #536 "Type-level literals as a
>> separate language extension" by Ross Paterson. Quick recap: currently
>> DataKinds controls promotion of ADTs and Symbol/Natural/Char literals. The
>> proposal is to factor out promotion of literals into their own extension,
>> TypeLevelLiterals.
>>
>> I recommended acceptance but received mixed feedback. Summary of opinions:
>> Vlad: "rec: accept"
>> SPJ: "content to accept"
>> Joachim: "unsure how that fits with the overall direction we have for
>> namespaces"
>> Arnaud: "unconvinced that it is worth yet one extra extension"
>> Richard: "pretty strongly against"
>> Adam: "avoid bundling together distinct features" (i.e. accept)
>> Chris: "in favour"
>> Iavor (as ex-member): "strongly in favor"
>>
>> Haven't yet expressed their opinion: Simon M. and Moritz.
>>
>> So we have roughly 5 votes in-favor-or-don't-mind and 3 votes
>> against-or-unconvinced. SPJ suggested that we simply count the votes, but
>> after reading the discussion, I find that there's a deeper reason for
>> disagreement. Essentially, we have two camps:
>>
>> 1. "Let a thousand flowers bloom": Haskell should be customizable, built
>> out of small extensions à la carte. (A necessary implication here is
>> that this gives rise to dialects of Haskell that depend on the set of
>> enabled extensions)
>> 2. "More extensions make me wince": Extensions are a necessary evil while
>> we explore the language design space, and we shouldn't create them
>> unnecessarily. (Language editions like GHC2021 help with that, allowing the
>> users to forget about individual extensions and simply use a better/newer
>> Haskell)
>>
>> The 1st paradigm suggests that TypeLevelLiterals should be factored out. TypeLevelLiterals+TypeData
>> form a dialect different from DataKinds with regards to name resolution,
>> which some users might prefer. Let them have it, why not?
>>
>> The 2nd paradigm suggests that breaking DataKinds into smaller extensions
>> is counterproductive. Do we want fewer extensions or more extensions, after
>> all? And as a steering committee, don't we have a clear direction in which
>> we steer?
>>
>> Unfortunately, we don't have a general policy that would clearly tell us
>> which camp/paradigm is right. And it's about time that we make a decision
>> regarding #536, even if we don't have a policy to guide us.
>>
>> Because of that, my new plan is to reject the proposal out of caution. We
>> have at least one "strongly against", and it's enough to give me pause.
>> It's probably better to stick to the status quo, at least until we develop
>> a concrete stance w.r.t. fine-grained extensions. (Pardon a digression, but
>> this also calls into question whether 448 is justified in splitting
>> ScopedTypeVariables into ExtendedForAllScope, MethodTypeVariables,
>> PatternSignatures. Maybe we don't want fine-grained extensions after all)
>>
>> The new recommendation is to reject the proposal, but I still can't make
>> this decision single-handedly. So let's do another round of discussion,
>> only this time let's stick to practicalities, not general considerations.
>> Is there anyone on the committee (or do we know someone) who needs TypeLevelLiterals
>> for practical reasons, not just as a matter of taste? For example,
>> 1. You are writing a book and you want to introduce TypeLevelLiterals
>> before DataKinds
>> 2. You are developing or maintaining a library or application that needs
>> TypeLevelLiterals but cannot use DataKinds
>> 3. You are working on an alternative Haskell implementation and intend to
>> support TypeLevelLiterals but not DataKinds
>>
>> If any of the above (or similar) applies, speak up.
>>
>> Vlad
>> _______________________________________________
>> 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.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-steering-committee/attachments/20231019/d326ddd3/attachment.html>