[GHC] #11438: Code does not compile without ScopedTypeVariables

[GHC]

#11438: Code does not compile without ScopedTypeVariables
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        Reporter:  wereHamster       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 We should also mention in the users guide the fact that type variables in
 an instance head are brought into scope.
 [[http://downloads.haskell.org/~ghc/master/users-
 guide//glasgow_exts.html?highlight=scoped%20type%20variables#ghc-flag--
 XScopedTypeVariables|Currently]] the text suggests that only variables
 introduced with an explicit `forall` are brought into scope.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11438#comment:2>
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