[GHC] #16139: GHC confused about type synonym kind with QuantifiedConstraints

[GHC]

#16139: GHC confused about type synonym kind with QuantifiedConstraints
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        Reporter:  Ashley Yakeley    |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      Resolution:                    |             Keywords:
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 RyanGlScott):

 You can work around this by annotating the result with a kind signature:

 {{{#!hs
 {-# LANGUAGE KindSignatures, RankNTypes, ConstraintKinds,
 QuantifiedConstraints #-}
 module Bug where
 import Data.Kind

 type E = (forall (a :: *). Eq a => Num a :: Constraint)
 }}}

 (FWIW, I am also confused as to why GHC doesn't just accept your
 definition as-is.)

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16139#comment:2>
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