[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      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by simonpj):

 The trouble is that I don't know how to do type inference in the presence
 of polymorphic constraints.  It is not a small change.

 It would be a useful feature. I've wanted it since at least 2000 (see
 [http://research.microsoft.com/en-us/um/people/simonpj/papers/derive.htm
 Derivable Type Classes]).

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/2893#comment:13>
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