[GHC] #5811: Compiler cannot deduce that type function is injective

[GHC]

#5811: Compiler cannot deduce that type function is injective
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  Reporter:  gatoatigrado      |          Owner:                  
      Type:  bug               |         Status:  closed          
  Priority:  normal            |      Milestone:                  
 Component:  Compiler          |        Version:  7.2.2           
Resolution:  invalid           |       Keywords:                  
        Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown      |     Difficulty:  Unknown         
  Testcase:                    |      Blockedby:                  
  Blocking:                    |        Related:                  
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Changes (by simonpj):

  * status:  new => closed
  * difficulty:  => Unknown
  * resolution:  => invalid


Comment:

 So just substitute!   GHC's consistent view is that instance '''heads'''
 must not overlap, without taking into account the instance context.   One
 could take a different view, but that would be a major major change
 (involving search, notably).

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5811#comment:1>
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