[ghc-steering-committee] Proposal: Or patterns #43 (Round 2)

[Simon Marlow]

+1, but we should hear from Simon about the existential point.

On 1 June 2018 at 08:30, Manuel M T Chakravarty <chak at justtesting.org>
wrote:

> We now have a revised version of the ”Or pattern” proposal #43 to consider:
>
>  (formatted) https://github.com/osa1/ghc-proposals/blob/or_
> patterns/proposals/0000-or-patterns.rst
>  (PR thread) https://github.com/ghc-proposals/ghc-proposals/pull/43
>
> You may remember that we discuss this a while back
>
>   https://mail.haskell.org/pipermail/ghc-steering-committee/
> 2017-November/000231.html
>
> and finally decided to bounce it back to the authors with the following
> recommendation:
>
>   https://github.com/ghc-proposals/ghc-proposals/pull/43#
> issuecomment-358189327
>
> We previously decided that we are inclined to accept this proposal if the
> authors change the points that we highlighted. Judging from the
> conversation of SimonPJ and Richard with the author on the GitHub thread,
> it appears to me that most of the issues have been addressed. However,
> Simon’s point
>
> • "Patterns that bind existentials, dictionaries, or equalities are
> rejected by the type checker". I disagree. Earlier I suggested "no variable
> bound by an or-pattern can have a type that mentions an existential
> variable bound by the or-pattern". That is much more friendly because you
> can still match against an existential constructor; you just can’t bind an
> existential variable.
>
> from <https://github.com/ghc-proposals/ghc-proposals/pull/43#
> issuecomment-368933401> still doesn’t seem to be addressed, or am I
> misunderstanding?
>
> Overall, I propose to accept the proposal, possibly requiring that the
> above point be addressed.
>
> What do you all think?
>
> Cheers,
> Manuel
>
>
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