[ghc-steering-committee] #621: Linear constraints, recommendation: accept

[Jakob Brünker]

Hi all,

There has been some discussion on the github thread since I presented this
to the committee, but it has now quieted down, so it would be great to get
some more opinions from you all on this proposal. So far I've only heard
from Sebastian.

Thanks,
Jakob

On Mon, Feb 17, 2025 at 9:40 AM Sebastian Graf <sgraf1337 at gmail.com> wrote:

> After multiple lengthy discussions that brought forth examples that IMO
> better motivate the proposal, I retract my earlier vote.
> However, since there are multiple points of design disagreement between
> Arnaud and me, I cannot vote in favour of acceptance either and will
> abstain from voting.
>
> Cheers,
> Sebastian
>
> Am Mo., 20. Jan. 2025 um 10:22 Uhr schrieb Sebastian Graf <
> sgraf1337 at gmail.com>:
>
>> I vote to return the proposal for revision. I listed my feedback in the
>> thread
>> <https://github.com/ghc-proposals/ghc-proposals/pull/621#issuecomment-2601848567>,
>> but the gist is:
>>
>> While I am sympathetic to the goal of introducing linearity annotations
>>> to constraints, simply because it is a logical extension of
>>> -XLinearTypes, I am afraid I do not feel motivated after having
>>> considered the examples in the proposal.
>>>
>> In fact, I think the examples overpromise on the utility of linear
>>> constraints and the problems it solves have simpler, more direct solutions.
>>
>>
>>  Cheers,
>> Sebastian
>>
>> Am Di., 14. Jan. 2025 um 23:45 Uhr schrieb Jakob Brünker <
>> jakob.bruenker at gmail.com>:
>>
>>> Dear committee,
>>>
>>> Arnaud Spiwack and Jack Hughes propose to introduce linear constraints.
>>>
>>> These work analogously to linear functions - as can be seen with the new
>>> syntax, which is %1 =>, reflecting the existing %1 ->. The motivation is
>>> that these constraints make it possible to design linearly typed APIs that
>>> are more convenient to use: Without the linear constraints, tokens would
>>> have to be passed manually into each function in these cases.
>>>
>>> The proposal also introduces dupable classes, which can be used multiple
>>> times even when they appear in a linear context, but cannot be passed to an
>>> unrestricted function. This is necessary to make some API designs work, see
>>> the proposal for details.
>>>
>>>
>>> To me, it seems that this proposal or something like it is necessary to
>>> unlock the full potential of linear types. The proposal lays out why
>>> monadic API designs don't provide the same benefits, and while there are
>>> potential future GHC developments that could make using it even more
>>> convenient (existential types, strict let improvements; see proposal), I
>>> believe it would already be sufficiently useful with today's GHC to be a
>>> valuable addition. Thus, I recommend acceptance.
>>>
>>> Please read through the proposal and voice your opinions.
>>>
>>> Best,
>>> Jakob
>>> _______________________________________________
>>> ghc-steering-committee mailing list
>>> ghc-steering-committee at haskell.org
>>> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee
>>>
>>
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