[GHC] #11275: :kind! doesn't reduce type families with poly-kinded return kinds

[GHC]

#11275: :kind! doesn't reduce type families with poly-kinded return kinds
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  GHCi           |           Version:  7.10.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Incorrect result
  Unknown/Multiple                   |  at runtime
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Originally discovered [https://mail.haskell.org/pipermail/ghc-
 devs/2015-December/010831.html here], here is a simplified example:

 {{{
 $ ghci
 GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
 λ> :set -XPolyKinds -XTypeFamilies
 λ> type family Hm :: k where Hm = Int
 λ> :kind! Hm
 Hm :: k
 = Hm
 }}}

 Giving `Hm` a monomorphic return kind of `*` makes it work with `:kind!`:

 {{{
 $ ghci
 GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
 λ> :set -XTypeFamilies
 λ> type family Hm :: * where Hm = Int
 λ> :kind! Hm
 Hm :: *
 = Int
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11275>
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