[GHC] #8026: DatatypeContexts should be fixed, not deprecated

[GHC]

#8026: DatatypeContexts should be fixed, not deprecated
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  Reporter:  gidyn             |          Owner:                  
      Type:  feature request   |         Status:  new             
  Priority:  normal            |      Milestone:                  
 Component:  Compiler          |        Version:  7.6.3           
Resolution:                    |       Keywords:                  
        Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown      |     Difficulty:  Unknown         
  Testcase:                    |      Blockedby:                  
  Blocking:                    |        Related:                  
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Comment(by monoidal):

 @gidyn: You probably meant `x :: Eq a => Pair a -> a`.

 Consider isaacdupree's `equal (undefined :: Pair (() -> ()))`. Surely this
 should be legal: `undefined` inhabits every type. Yet attempting to
 evaluate it leads to using `==` from `Eq (() -> ())` which does not exist.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/8026#comment:9>
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