[GHC] #15316: Regarding coherence and implication loops in presence of QuantifiedConstraints

[GHC]

#15316: Regarding coherence and implication loops in presence of
QuantifiedConstraints
-------------------------------------+-------------------------------------
        Reporter:  mniip             |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  high              |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.5
  checker)                           |             Keywords:
      Resolution:                    |  QuantifiedConstraints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC accepts       |            Test Case:  quantified-
  invalid program                    |  constraints/T15316
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by simonpj):

 * status:  new => merge
 * testcase:   => quantified-constraints/T15316


Comment:

 OK, so now you need `UndecidableInstances` to have bad quantified
 constraints, just as the original proposal said.

 Probably worth merging, not crucial

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15316#comment:9>
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