[GHC] #4426: Simplify the rules for implicit quantification

[GHC]

#4426: Simplify the rules for implicit quantification
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        Reporter:  simonpj           |                Owner:  bgamari
            Type:  feature request   |               Status:  closed
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  6.12.3
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #7880             |  Differential Rev(s):  Phab:D211,
       Wiki Page:                    |  Phab:D1615
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Comment (by simonpj):

 Ah well, GHC 8.0 implements the simpler quantification rules, and now just
 says
 {{{
 T4426.hs:5:29: error: Not in scope: type variable `b'
 }}}
 which at least isn't misleading!

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4426#comment:31>
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