[GHC] #13333: Typeable regression in GHC HEAD

[GHC]

#13333: Typeable regression in GHC HEAD
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        Reporter:  RyanGlScott       |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:  typeable
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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Comment (by bgamari):

 Looking at `-ddump-tc-trace` from the program in the ticket description,
 it seems that we are failing to solve for this,
 {{{
 WC {wc_simple =
       [WD] $dTypeable_a29a
         {0}:: Typeable (T |> Trans (Sym cobox ->_N <*>_N)
                                    (cobox ->_N <*>_N)) (CDictCan)}
 }}}
 I believe the reason for this is that we don't handle casts in the
 `Typeable` solver. I'll need to think about this.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13333#comment:5>
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