[GHC] #8390: regression in handling of type variables in constraints on instances which do not appear in the instance head

[GHC]

#8390: regression in handling of type variables in constraints on instances which
do not appear in the instance head
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        Reporter:  aavogt                     |            Owner:
            Type:  bug                        |           Status:  closed
        Priority:  normal                     |        Milestone:
       Component:  Compiler                   |          Version:  7.7
      Resolution:  invalid                    |         Keywords:
Operating System:  Unknown/Multiple           |     Architecture:
 Type of failure:  GHC rejects valid program  |  Unknown/Multiple
       Test Case:                             |       Difficulty:  Unknown
        Blocking:                             |       Blocked By:
                                              |  Related Tickets:
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Changes (by aavogt):

 * status:  new => closed
 * resolution:   => invalid


Comment:

 I found -XAllowAmbiguousTypes, added by commit
 97db0edc4e637dd61ec635d1f9b6b6dd25ad890c, which allows the old behavior.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8390#comment:3>
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