[GHC] #15359: Quantified constraints do not work with equality constraints

[GHC]

#15359: Quantified constraints do not work with equality constraints
-------------------------------------+-------------------------------------
        Reporter:  goldfire          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:
                                     |  QuantifiedConstraints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by RyanGlScott):

 It's very strange to me that we allow quantified `Coercible` constraints
 but not quantified `(~)` constraints. What is the rationale behind this
 decision choice?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15359#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler