[GHC] #16252: QuantifiedConstraints: lack of inference really is a problem

[GHC]

#16252: QuantifiedConstraints: lack of inference really is a problem
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        Reporter:  lightandlight     |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.2
      Resolution:                    |             Keywords:
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 lightandlight):

 Okay, I've thought about this for a little bit:

 Why shouldn't the implication constraint be considered part of
 `quant_pred_candidates`? It seems to me that the error is in discarding it
 as a candidate in the first place. In other words, I would expect `g`'s
 inferred type to be `(forall x. Eq x => Eq (f x)) => A f -> A f -> Bool`.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16252#comment:3>
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