[GHC] #9440: Buggy binder swap in occurrence analysis

[GHC]

#9440: Buggy binder swap in occurrence analysis
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              Reporter:  afarmer     |            Owner:
                  Type:  bug         |           Status:  patch
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D156   |
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Comment (by simonpj):

 That's terrible!  Than you for spotting this.

 Re (a), I'm not sure how convenient it is to check that `x` is free in `C
 vs -> rhs`.  Perhaps it is easy.  But if not, you could instead just check
 that `x` is not in `vs`.  That could conveniently be done with checking
 (b).

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9440#comment:3>
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