[GHC] #7938: Unbound kind variable can appear in RHS of associated type

[GHC]

#7938: Unbound kind variable can appear in RHS of associated type
----------------------------------------+-----------------------------------
Reporter:  goldfire                     |          Owner:  goldfire        
    Type:  bug                          |         Status:  new             
Priority:  normal                       |      Component:  Compiler        
 Version:  7.6.3                        |       Keywords:                  
      Os:  Unknown/Multiple             |   Architecture:  Unknown/Multiple
 Failure:  GHC accepts invalid program  |      Blockedby:                  
Blocking:                               |        Related:                  
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 Consider the following code:

 {{{
 {-# LANGUAGE TypeFamilies, PolyKinds, MultiParamTypeClasses,
              FlexibleInstances, DataKinds #-}

 data KProxy (a :: *) = KP

 class Foo (a :: k1) (b :: k2) where
   type Bar a

 instance Foo (a :: k1) (b :: k2) where
   type Bar a = (KP :: KProxy k2)
 }}}

 The kind variable {{{k2}}} appears on the RHS of the instance for
 {{{Bar}}} but not on the left-hand side. This is disallowed for type
 variables, but there seems to be no check for kind variables.

 I will fix in an upcoming patch.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7938>
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