[ghc-steering-committee] Recommendation: reject #367 (was: Re: Please review #367: Clarify primops using unboxed sums, Shepherd: Simon Marlow)

[Simon Marlow]

Committee,

Proposal #367 suggests using unboxed sums for the results of 7 (seven)
primops that use sum types but currently have to encode those explicitly
using `Int#`.

https://github.com/treeowl/ghc-proposals/blob/unboxed-sum-primops/proposals/0000-unboxed-sum-primops.md

The proposal is arguably the right thing, however I'm suggesting we reject
it for the following reasons:

   1. The implementations of the primops would bake in the translation of
   unboxed sums. Right now our unboxed sum translation is defined in one place
   - CorePrep - but this proposal would leak it into the implementations of a
   few primops.
   2. Migration would entail adding a backwards-compatibility layer, with
   the associated complexity and risk of performance regressions.
   3. While the current situation is perhaps inelegant, it's not broken and
   it's easy to understand.

Thoughts?

Simon


On Sun, 4 Oct 2020 at 22:14, Joachim Breitner <mail at joachim-breitner.de>
wrote:

> Dear Committee,
>
> this is your secretary speaking:
>
> Clarify primops using unboxed sum
> has been proposed by David Feuer
> https://github.com/ghc-proposals/ghc-proposals/pull/367
>
> https://github.com/treeowl/ghc-proposals/blob/unboxed-sum-primops/proposals/0000-unboxed-sum-primops.md
>
> I’ll propose Simon Marlow as the shepherd.
>
> Please guide us to a conclusion as outlined in
> https://github.com/ghc-proposals/ghc-proposals#committee-process
>
> Thanks,
> Joachim
> --
> Joachim Breitner
>   mail at joachim-breitner.de
>   http://www.joachim-breitner.de/
>
>
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