[GHC] #10116: Closed type families: Warn if it doesn't handle all cases

[GHC]

#10116: Closed type families: Warn if it doesn't handle all cases
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        Reporter:  andrewthad        |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.8.4
      Resolution:                    |             Keywords:
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 gkaracha):

 Replying to [comment:11 goldfire]:
 > `G` is inhabited at the type level, by `Any` for example.

 Oh, I see, right, Yet, both `Any` and `Loopy` need `UndecidableInstances`.
 Is there a way to inhabit `G` without enabling `UndecidableInstances`?

 I expect a good check to be able to handle everything anyway, I am just
 asking in an attempt to identify a subset of the language for which the
 check can have nice properties. :-)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10116#comment:12>
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