[GHC] #6020: "Couldn't match kind" with free type variables and PolyKinds

[GHC]

#6020: "Couldn't match kind" with free type variables and PolyKinds
---------------------------------------+------------------------------------
 Reporter:  atnnn                      |          Owner:                  
     Type:  feature request            |         Status:  new             
 Priority:  normal                     |      Component:  Compiler        
  Version:  7.5                        |       Keywords:                  
       Os:  Unknown/Multiple           |   Architecture:  Unknown/Multiple
  Failure:  GHC rejects valid program  |       Testcase:                  
Blockedby:                             |       Blocking:                  
  Related:                             |  
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Comment(by atnnn):

 Pinning the kind makes the instance work:

 {{{
 instance (Id x y, Id y z) => Test x (z :: Bool)
 }}}

 But using kind variables doesn't:

 {{{
 instance (Id x (y :: k), Id y z) => Test x (z :: k)
 }}}

 {{{
 Not in scope: type variable `k'
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6020#comment:1>
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