[GHC] #13621: Problems with injective type families

[GHC]

#13621: Problems with injective type families
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  InjectiveFamilies
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 No, injectivity can't yet do this. Injectivity annotations are very much
 like functional dependencies, working only to do type inference. They have
 no representation in Core. Why not, you ask? Because I was unable to prove
 the soundness of doing so. But perhaps
 [http://cs.brynmawr.edu/~rae/papers/2017/partiality/partiality.pdf
 Constrained Type Families] gives us a way forward here. I have yet to
 attempt the injectivity proof in the context of that paper, but my hunch
 is that it will succeed.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13621#comment:1>
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