[GHC] #14860: QuantifiedConstraints: Can't quantify constraint involving type family

[GHC]

#14860: QuantifiedConstraints: Can't quantify constraint involving type family
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.5
  checker)                           |             Keywords:
      Resolution:  wontfix           |  QuantifiedConstraints wipT2893
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Iceland_jack):

 An example, from [https://www.microsoft.com/en-us/research/wp-
 content/uploads/2016/02/jfp-outsidein.pdf OutsideIn(X)] (**2.4**), this
 function

 {{{#!hs
 h :: forall a. (forall b. FB a b ~ Bool) => Bar a -> Bool
 }}}

 Details in
 [https://gist.github.com/Icelandjack/aeda8e98214cc52c96230af7b8724d25
 gist].

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14860#comment:16>
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