[GHC] #9301: Rank-2 constraints are assigned kind *

[GHC]

#9301: Rank-2 constraints are assigned kind *
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        Reporter:  heisenbug         |            Owner:
            Type:  bug               |           Status:  closed
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.8.2
      Resolution:  duplicate         |         Keywords:
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/9301#comment:5>
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