[GHC] #4807: Data instance for Data.Map is incomplete

[GHC]

#4807: Data instance for Data.Map is incomplete
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    Reporter:  sclv              |       Owner:                             
        Type:  bug               |      Status:  new                        
    Priority:  normal            |   Component:  libraries/base             
     Version:  7.0.1             |    Keywords:                             
    Testcase:                    |   Blockedby:                             
          Os:  Unknown/Multiple  |    Blocking:                             
Architecture:  Unknown/Multiple  |     Failure:  Incorrect result at runtime
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Comment(by sclv):

 I realized after submitting this ticket that it could go either way. I
 tend to think that it should still be possible to define a proper
 dataCast1, since its certainly easier to use ext1 for partially
 specialized maps than it is to use ext2 and enforce some of the
 specialization by hand. However, these things are feasible, if painful,
 with ext2, and I can't offhand write the dataCast1 instance myself.

 If one is feasible to write, then I think its a no-brainer to add it. If
 it seems hard-to-impossible to write, then now we have the ext2 functions,
 and I agree that this is sufficient.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4807#comment:2>
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