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
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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