[GHC] #16313: Core Lint warning (Unsafe coercion: {left, right}-hand type is levity-polymorphic)

[GHC]

#16313: Core Lint warning (Unsafe coercion: {left,right}-hand type is levity-
polymorphic)
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      Resolution:                    |             Keywords:
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 goldfire):

 Hrm. Maybe I was too quick to say that any bleating from core-lint meant
 we have a GHC bug. I've never been comfortable with this sort of check,
 really. I advocate dropping the check... or finding a way to suppress the
 warning.

 Simon, this comes from #9122, where you wanted to institute this sorts of
 checks. The problem is that there's no way of getting rid of the warning
 (while keeping the more important `-dcore-lint` checks enabled).

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16313#comment:1>
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