[GHC] #11552: ScopedTypeVariables / InstanceSigs do not work in GHC 8.0

[GHC]

#11552: ScopedTypeVariables / InstanceSigs do not work in GHC 8.0
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        Reporter:  bitemyapp         |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.0.1-rc1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 Not sure whether this change was intentional, but you don't need the
 `forall f .`, and the code compiles fine without it. See
 http://ghc.readthedocs.org/en/latest/glasgow_exts.html#class-and-instance-
 declarations.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11552#comment:2>
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