[Haskell-cafe] Proposal: Instance apartness guards
olshanskydr at gmail.com
Thu Nov 9 09:08:22 UTC 2017
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
2017-11-08 12:29 GMT+03:00 Anthony Clayden <anthony_clayden at clear.net.nz>:
> 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
> Thank you
> ----- 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.
> > AntC
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