Re: [GHC] #12369: data families shouldn't be required to have return kind *, data instances should

27 Jul 2017

      #12369: data families shouldn't be required to have return kind *, data instances
should
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        Reporter:  ekmett            |                Owner:  (none)
            Type:  feature request   |               Status:  closed
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:  fixed             |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:  indexed-
                                     |  types/should_compile/T12369
      Blocked By:                    |             Blocking:
 Related Tickets:  #14045            |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by RyanGlScott):

 * related:   => #14045

Comment:

 By the way, the commit message for
 4239238306e911803bf61fdda3ad356fd0b42e05 claims:

 {{{
 - A data instance need not list all patterns, much like how a
   GADT-style data declaration need not list all type parameters,
   when a kind signature is in place. This is useful, for example,
   here:

     data family Sing (a :: k)
     data instance Sing :: Bool -> Type where ...
 }}}

 I just tried this recently, and that example doesn't actually work. To
 avoid cluttering this ticket further, I've spun this off into #14045.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12369#comment:16
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