[GHC] #9558: "Illegal equational constraint" that might not be the users fault

[GHC]

#9558: "Illegal equational constraint" that might not be the users fault
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              Reporter:  rrnewton    |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.9
            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:              |
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Comment (by rwbarton):

 > Is this a GHC bug in 7.9 or in 7.8?

 Neither really, this is an intentional change in behavior, see #8883.
 (Though I personally question whether it is worth breaking existing code
 for a rather intangible benefit.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9558#comment:1>
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