[GHC] #12432: TypeInType: open type family application as type family return kind fails to compile

[GHC]

#12432: TypeInType: open type family application as type family return kind fails
to compile
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        Reporter:  j6carey           |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:  duplicate         |             Keywords:
Operating System:  Linux             |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 This example also has another problem: forgetting about lifted equality
 and such, an associated type cannot assume any context of an instance.
 This is because an associated type instance is effectively floated out of
 the class and behaves identically to a standalone type instance.
 Associated types just give you some nice syntax -- and that's it.... but
 maybe we need to revisit all of this, and perhaps allow type instances to
 specify a context.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12432#comment:5>
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