[ghc-steering-committee] #526: Applicative Comprehensions (rec: accept)

[Adam Gundry]

I'm unconvinced by the current state of this proposal, for similar 
reasons as Simon PJ gives on the proposal thread 
(https://github.com/ghc-proposals/ghc-proposals/pull/526#issuecomment-1740735610).

If we want to accept this merely for reasons of consistency, I think the 
simplest way forward would be to not introduce a new extension name, and 
instead define the combination of MonadComprehensions + ApplicativeDo to 
do what the proposal suggests.

The author doesn't seem to be responsive on the thread. While I worry 
this may be because of the time the proposal process has been taking, it 
makes it difficult to gauge support for the various alternative 
suggestions that have been made.

Cheers,

Adam


On 28/09/2023 08:12, Simon Marlow wrote:
> Dear committee,
> 
> #526 proposes a new extension ApplicativeComprehensions (implying 
> MonadComprehensions). It would provide the equivalent of the current 
> ApplicativeDo desugaring for do-expressions to list comprehensions.
> 
>   * Github thread <https://github.com/ghc-proposals/ghc-proposals/pull/526>
>   * Rendered
>     <https://github.com/strake/ghc-proposals/blob/acomp/proposals/0000-applicative-comprehensions.rst>
> 
> The extension itself is relatively uncontroversial, but there are some 
> unresolved quirks in the original ApplicativeDo extension which made us 
> uneasy about extending it. However, after various discussions I'm going 
> to propose accepting this proposal in its current state.  Rationale:
> 
>   * It doesn't make things worse, and the implementation isn't likely to
>     add significant complexity.
>   * It retains consistency between ApplicativeDo and
>     ApplicativeComprehensions (in contrast to the idea of making
>     ApplicativeComprehensions perform a simpler desugaring, which came
>     up during the discussion)
>   * A future proposal can add a simpler version of the desugaring for
>     both extensions later.
> 
> 
> Cheers
> Simon

-- 
Adam Gundry, Haskell Consultant
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