[GHC] #14331: Overzealous free-floating kind check causes deriving clause to be rejected

[GHC]

#14331: Overzealous free-floating kind check causes deriving clause to be rejected
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.2.1
  checker)                           |
      Resolution:                    |             Keywords:  deriving
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 So, if `deriving (C (a :: k))` doesn't mean to quantify, what do you
 expect it to mean? I agree that the current error is wrong, but I'm not
 sure what behavior you want GHC to take here.

 If you want GHC to accept your original declaration, creating `instance
 forall k (a :: k). C a D`, then we're basically in agreement.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14331#comment:4>
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