[GHC] #12018: Equality constraint not available in pattern type signature (GADTs/ScopedTypeVariables)

[GHC]

#12018: Equality constraint not available in pattern type signature
(GADTs/ScopedTypeVariables)
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  lowest            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.10.3
  checker)                           |             Keywords:  GADTs,
      Resolution:                    |  ScopedTypeVariables
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 RyanGlScott):

 Ah, thank you for those examples, Simon. I was imaging GADT pattern-
 matching to be a sort of "whole-case" operation, but that is clearly not
 the case, as `f` demonstrates. So I think I'm barking up the entirely
 wrong tree with what I was requesting in comment:5.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12018#comment:9>
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