[GHC] #13962: GHCi allows unsaturated type family

[GHC]

#13962: GHCi allows unsaturated type family
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #12089            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 The muddiness all comes down to this: If GHC knows `m a ~ Maybe Int`,
 should it choose `m ~ Maybe` and `a ~ Int`? After all, if `m` could be an
 unsaturated type family, committing to the above decomposition would be
 wrong.

 This kind of inference seems unlikely in `:kind` or `:kind!`, though I
 can't rule it out if someone tried to.

 In the end, I think we should just keep the current behavior.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13962#comment:5>
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