[GHC] #12766: Allow runtime-representation polymorphic data families

[GHC]

#12766: Allow runtime-representation polymorphic data families
-------------------------------------+-------------------------------------
           Reporter:  Iceland_jack   |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:  TypeInType     |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #12369
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 This is an offshoot of #12369 (‘ data families shouldn't be required to
 have return kind *, data instances should’), allowing family declarations
 something like:

 {{{#!hs
 data family Array a :: TYPE rep
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12766>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler