[GHC] #14420: Data families should not instantiate to non-Type kinds

3 Nov 2017

      #14420: Data families should not instantiate to non-Type kinds
-------------------------------------+-------------------------------------
           Reporter:  goldfire       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{#!hs
 data family Any :: k  -- allowable now due to fix for #12369

 type family F (a :: Bool) :: Nat where
   F True  = 0
   F False = 1
   F Any   = 2
 }}}

 {{{
 ghci> :kind! F True
 F True :: Nat
 = 0
 ghci> :kind! F False
 F False :: Nat
 = 1
 ghci> :kind! F Any
 F Any :: Nat
 = 2
 }}}

 Oh dear.

 We should require that any instantiation of a data family be to a kind
 that ends in `Type`.

 Inspired by comment:31:ticket:9429

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14420
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