[GHC] #9729: GHCi accepts invalid programs when recompiling

[GHC]

#9729: GHCi accepts invalid programs when recompiling
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        Reporter:  crockeea          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  GHCi              |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by ezyang):

 * version:  7.8.3 => 8.0.1


Comment:

 Unfortunately, I was able to reproduce with GHC 8.0.1, so I guess the
 visibility changes were not enough. Could it be that `~` instances are
 treated specially? Investigation necessary!

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9729#comment:6>
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