[GHC] #14845: TypeInType, index GADT by constraint witness

[GHC]

#14845: TypeInType, index GADT by constraint witness
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13895            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 Technically, we do promote `S`, but the promoted `S` can't ever be
 applied, because we can't produce evidence. Perhaps a better error message
 is warranted, but until we have real dependent types (and can promote
 dictionaries), I think we're stuck on this one.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14845#comment:4>
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