[GHC] #13549: GHC 8.2.1's typechecker rejects code generated by singletons that 8.0 accepts

[GHC]

#13549: GHC 8.2.1's typechecker rejects code generated by singletons that 8.0
accepts
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
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:                    |
-------------------------------------+-------------------------------------
Changes (by RyanGlScott):

 * priority:  high => normal
 * milestone:  8.2.1 => 8.4.1


Comment:

 You are correct that adding more type signatures to the `where`-bound
 functions of `permutations` (specifically, `interleave'`) resolves the
 issue upstream in `singletons`. Given that there's a viable workaround,
 I'm going to reduce the priority of this ticket.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13549#comment:12>
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