Re: Proposal: Instance apartness guards

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Re: Proposal: Instance apartness guards

Dmitry Olshansky
Dear Anthony C & Richard E!

From my side (as GHC-user) it definitely looks like the much more natural way than OverlappedInstances (say, +1). 
Unfortunately I am not an expert and can only ask with you for feedback from experts.

Dmitry


2017-11-08 12:29 GMT+03:00 Anthony Clayden <[hidden email]>:
Surprisinlgy little comment on this proposal.
Perhaps it landed when yous were busy elsewhere.
I'd like to push it to the committee soon;
this is an invitation for more feedback.

Richard E wrote a nice brief summary
https://github.com/ghc-proposals/ghc-proposals/pull/56#issuecomment-311421457

Thank you
AntC


----- Original Message Follows -----
> After years of pondering this idea (in various forms),
> and several rounds of discussion on several forums,
> I've written it up.
>
> "This proposal tackles the thorny topic of Overlapping
> instances,
>  for both type classes and Type Families/Associated types,
>  by annotating instance heads with type-level apartness
> Guards.
>  Type-level disequality predicates appear in Sulzmann &
> Stuckey 2002;
>  in the type-level ‘case selection’ in HList 2004;
>  and in various guises in Haskell cafe discussions in
> following years.
>  This proposal builds on the apartness testing implemented
>  as part of the Closed Type Families work."
>
> All feedback welcome.
>
>
https://github.com/AntC2/ghc-proposals/blob/instance-apartness-guards/proposals/0000-instance-apartness-guards.rst
>
> AntC
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