[GHC] #9858: Typeable instances should be kind-aware

[GHC]

#9858: Typeable instances should be kind-aware
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        Reporter:  dreixel           |                   Owner:  dreixel
            Type:  bug               |                  Status:  new
        Priority:  highest           |               Milestone:  7.10.1
       Component:  Compiler          |                 Version:  7.9
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by goldfire):

 I vote for Simon's option 1 -- just make runtime type identification a
 feature of GHC Haskell, exposed through the `Typeable` interface. This
 will take a small amount of work to engineer, but I think the end state
 will be simpler than what we have now, and likely more efficient.

 I will point out one drawback: I believe users will be confused about the
 need for `Typeable` constraints. After all, if ''every'' type is
 `Typeable`, then why include the constraint? We cognoscenti know that the
 `Typeable` constraint is just implicitly passing the runtime witness, but
 we'll have to be careful to explain this to those who think that class
 constraints are all about logical statements, not implicit type-determined
 parameters.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9858#comment:21>
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