[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:  task        |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.8.4
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
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 Right now, I can do the following:

 data Foo = A | B
 type family Bar (n :: 'Foo) where
   Bar 'A = Int

 I would like to be warned if I write a partial type function like this
 because partial functions are almost always a mistake.

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