[GHC] #14863: QuantifiedConstraints: Can't deduce `c' from `(a, b)' and `a |- b |- c'

[GHC]

#14863: QuantifiedConstraints: Can't deduce `c' from `(a, b)' and `a |- b |- c'
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:
                                     |  QuantifiedConstraints wipT2893
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 simonpj):

 Yes; and I've added a test case
 {{{
 commit 32e8499889d314e9efd0747b4053290a2dc237d5
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Fri Mar 2 22:53:27 2018 +0000

     Test Trac #14863
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14863#comment:4>
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