[GHC] #15683: coerce fails for Coercible type families

[GHC]

#15683: coerce fails for Coercible type families
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.6.1
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by sam-barr):

 For reference, I (the OP of the reddit post) encountered this issue when
 trying to use idioms introduced in Trees That Grow. It would be useful to
 be able to coerce subtrees without explicit recursion when no further
 manipulation is required.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15683#comment:2>
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