[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 goldfire):

 `G` is inhabited at the type level, by `Any` for example. And by

 {{{#!hs
 type family Loopy :: G where
   Loopy = MkG Loopy
 }}}

 Normally, using something like `Loopy` in a program will cause GHC to
 issue an error, but sufficient cleverness can get this past the type-
 checker. So I would say your `F`'s equation is not redundant at all.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10116#comment:11>
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