[GHC] #7643: Kind application error

[GHC]

#7643: Kind application error
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Reporter:  gmainland         |          Owner:                         
    Type:  bug               |         Status:  new                    
Priority:  normal            |      Component:  Compiler (Type checker)
 Version:  7.6.1             |       Keywords:                         
      Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple       
 Failure:  None/Unknown      |      Blockedby:                         
Blocking:                    |        Related:  #7354                  
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Changes (by shachaf):

  * related:  => #7354


Comment:

 I reduced the test case a bit:

 {{{
 {-# LANGUAGE MagicHash, TypeFamilies #-}

 module T7643 where

 import GHC.Exts

 type family T
 type instance T = RealWorld

 foo :: () -> State# T
 foo _ = unsafeCoerce# realWorld#
 }}}

 The `unsafeCoerce#`ed type actually matches -- but GHC has a problem with
 `State# RealWorld ~ State# T` (this isn't specific to `State#` or
 `RealWorld` -- unboxed tuples etc. work too. The issue is with the kinds).

 This seems to be a variety of #7354, but it's still broken in HEAD because
 of the kind issue.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7643#comment:1>
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