[GHC] #12239: Dependent type family does not reduce

[GHC]

#12239: Dependent type family does not reduce
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        Reporter:  int-index         |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |             Keywords:  TypeInType,
      Resolution:                    |  TypeFamilies
Operating System:  Unknown/Multiple  |         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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Changes (by int-index):

 * priority:  normal => high
 * milestone:   => 8.2.1


Comment:

 I'm raising the priority and setting the milestone to 8.2 since 8.2 is a
 consolidation release and I would love to see the bug fixed.

 Tried to fix it myself but after a few hours of reading GHC source I
 realized that I lack the necessary expertise (although I could try again
 if someone was to mentor me).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12239#comment:6>
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