[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:  closed          
  Priority:  normal                     |      Milestone:                  
 Component:  Compiler                   |        Version:  7.5             
Resolution:  fixed                      |       Keywords:                  
        Os:  Unknown/Multiple           |   Architecture:  Unknown/Multiple
   Failure:  GHC rejects valid program  |     Difficulty:  Unknown         
  Testcase:  polykinds/T6020, T6020a    |      Blockedby:                  
  Blocking:                             |        Related:                  
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Changes (by simonpj):

  * status:  new => closed
  * testcase:  polykinds/T6020 => polykinds/T6020, T6020a
  * resolution:  => fixed


Comment:

 Urgh.  A one-character typo! Fixed by
 {{{
 commit 4cc882650af6a4fadb30706f21e987edb846bcc3
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Thu Apr 26 09:29:15 2012 +0100

     Fix a one-character typo (kv1 should be kv2!)

     Fixes Trac #6020, #6044
 >---------------------------------------------------------------

  compiler/typecheck/TcUnify.lhs |    2 +-
  1 files changed, 1 insertions(+), 1 deletions(-)

 diff --git a/compiler/typecheck/TcUnify.lhs
 b/compiler/typecheck/TcUnify.lhs index 1729dcd..6e4d128 100644
 --- a/compiler/typecheck/TcUnify.lhs
 +++ b/compiler/typecheck/TcUnify.lhs
 @@ -1119,7 +1119,7 @@ uKVar isFlipped unify_kind eq_res kv1 k2
    | TyVarTy kv2 <- k2, kv1 == kv2
    = return eq_res

 -  | TyVarTy kv2 <- k2, isTcTyVar kv1, isMetaTyVar kv2
 +  | TyVarTy kv2 <- k2, isTcTyVar kv2, isMetaTyVar kv2
    = uKVar (not isFlipped) unify_kind eq_res kv2 (TyVarTy kv1)

    | otherwise = if isFlipped
 }}}
 I added a new regression test too!

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6020#comment:5>
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