[GHC] #7102: Type family instance overlap accepted in ghci

[GHC]

#7102: Type family instance overlap accepted in ghci
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        Reporter:  exbb2             |                Owner:  rwbarton
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  GHCi              |              Version:  7.4.1
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:  T7102a, T7102
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2994
       Wiki Page:                    |
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Comment (by oerjan):

 Perhaps the error message for the instance overlap could mention (if in
 GHCi) that you can get around it by redeclaring the type family.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7102#comment:13>
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