[GHC] #14584: Core Lint error

[GHC]

#14584: Core Lint error
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  TypeInType,
                                     |  DeferredTypeErrors
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):

 Why doesn't `co2` float out? We really shouldn't float `co1` out if we
 don't float `co2` out. The fact that it works without deferred type errors
 is just a fluke, really. (What if `co2` ends up being filled in with a
 coercion that mentions `x`?)

 I think this can be fixed just by adding a little more logic to the float-
 out code. Unfortunately, it also means that we need to calculate floating-
 out in dependency order (so we can process `co2` before even looking at
 `co1`. It makes the floating-out code a little more intricate, but the
 complication should be quite local.

 Does that sound reasonable?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14584#comment:4>
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