[GHC] #8105: unhelpful error message PolyKinds + GADTs

[GHC]

#8105: unhelpful error message PolyKinds + GADTs
-------------------------+-------------------------------------------------
       Reporter:  wvv    |             Owner:
           Type:  bug    |            Status:  new
       Priority:         |         Milestone:
  normal                 |           Version:  7.6.3
      Component:         |  Operating System:  Unknown/Multiple
  Compiler               |   Type of failure:  Incorrect warning at
       Keywords:         |  compile-time
   Architecture:         |         Test Case:
  Unknown/Multiple       |          Blocking:
     Difficulty:         |
  Unknown                |
     Blocked By:         |
Related Tickets:         |
-------------------------+-------------------------------------------------
 For
 {{{
 data Foo (a::k) = Foo a
 }}}
 we have next right error:
 {{{
     Kind mis-match
     Expected kind `OpenKind', but `a' has kind `k'
     In the type `a'
     In the definition of data constructor `Foo'
     In the data declaration for `Foo'
 }}}

 but for same GADTs data we have just
 {{{
 data Foo (a::k) where
     Foo a :: Foo a

 <interactive>:38:27: parse error on input `a'
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8105>
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