[GHC] #5667: Data.Unique.Unique and Data.Graph.SCC are not instances of Show

[GHC]

#5667: Data.Unique.Unique and Data.Graph.SCC are not instances of Show
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    Reporter:  jewillco          |       Owner:                
        Type:  feature request   |      Status:  new           
    Priority:  normal            |   Component:  libraries/base
     Version:  7.2.1             |    Keywords:                
    Testcase:                    |   Blockedby:                
          Os:  Unknown/Multiple  |    Blocking:                
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown  
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Comment(by jewillco):

 It turns out that the instance for `Unique` needs to be written manually
 (using `hashUnique`) outside its module, but it can probably derived in
 `Data.Unique` because that module has access to the constructor(s) of
 `Unique`.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5667#comment:1>
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