[GHC] #15305: Erroneous "non-exhaustive pattern match" using nested GADT with strictness annotation

[GHC]

#15305: Erroneous "non-exhaustive pattern match" using nested GADT with strictness
annotation
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        Reporter:  jkoppel           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  Research
       Component:  Compiler (Type    |  needed
  checker)                           |              Version:  8.4.3
      Resolution:                    |             Keywords:
                                     |  PatternMatchWarnings
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 > I fail to see how this would work for recursive examples like the
 program in comment:7

 Correct.  Computing `NonVoid( tau )` is an open-ended question. For some
 `tau`s (lke `Bar A`) it's easy; for others we could be more ambitious.
 It's probably undecidable in general.

 So we could start with something simple and become more ambitious later.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15305#comment:11>
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