[GHC] #13604: regression in ghc 8.2.1-rc1 (8.2.0.20170404)

[GHC]

#13604: regression in ghc 8.2.1-rc1 (8.2.0.20170404)
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        Reporter:  George            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  GHCi              |              Version:  8.2.1-rc1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Whether or not it is the "right" behaviour, it would be good if the user
 manual documented the behaviour and the underlying principles.  And
 describes how to work around it if you want something different.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13604#comment:12>
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