[GHC] #13105: Allow type families in RuntimeReps

[GHC]

#13105: Allow type families in RuntimeReps
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        Reporter:  goldfire          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  LevityPolymorphism
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  typecheck/should_fail/T13105
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 I was thinking of this as an adjunct to the LP test in the desugarer.  If
 the argument of an application has type `ty :: TYPE k`, and `k` does not
 pass the LP test (yet), then normalise `k` (using top level instances
 only) and cast the arg wtih a coercion `TYPE k ~ TYPE k_norm`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13105#comment:5>
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