[GHC] #4966: Type checking regression

[GHC]

#4966: Type checking regression
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    Reporter:  igloo                    |        Owner:  simonpj                      
        Type:  bug                      |       Status:  merge                        
    Priority:  highest                  |    Milestone:  7.0.2                        
   Component:  Compiler (Type checker)  |      Version:  7.0.1                        
    Keywords:                           |     Testcase:  deriving/should_compile/T4966
   Blockedby:                           |   Difficulty:                               
          Os:  Unknown/Multiple         |     Blocking:                               
Architecture:  Unknown/Multiple         |      Failure:  None/Unknown                 
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Changes (by simonpj):

  * status:  new => merge
  * testcase:  => deriving/should_compile/T4966


Comment:

 Fixed by
 {{{
 Thu Feb 17 14:10:00 GMT 2011  simonpj at microsoft.com
   * Fix Trac #4966

   This is just a program that exploits overlapping
   instances in a delicate way. The fix makes GHC
   a bit more friendly towards such programs.

   See Note [Overlap and deriving] in TcSimplify

     M ./compiler/typecheck/TcSimplify.lhs -5 +30
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4966#comment:3>
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