[GHC] #2893: Implement "Quantified contexts" proposal

[GHC]

#2893: Implement "Quantified contexts" proposal
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        Reporter:  porges            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  ⊥
       Component:  Compiler          |              Version:  6.10.1
      Resolution:                    |             Keywords:  proposal
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 Iceland_jack):

 Replying to [comment:20 RyanGlScott]:
 > 2. What does it mean to automatically generate instances for `(:=>)`?

 That is the question isn't it, I imagined it as `Typeable` or `Coercible`
 where the compiler creates instances on the fly but which instances I do
 not know.

 > While those classes are neat tricks that can get you some of the
 functionality of `QuantifiedConstraints`/`ImplicationConstraints`, they
 don't go all the way.

 `QuantifiedConstraints` and `ImplicationConstraints` would certainly be
 preferable! Are there any plans to research / implement such features?
 They would enable a lot of awesome code that is currently beyond reach.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/2893#comment:21>
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