[GHC] #15192: Refactor of Coercion

[GHC]

#15192: Refactor of Coercion
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        Reporter:  ningning          |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4747
       Wiki Page:                    |
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Comment (by goldfire):

 As a follow-on to comment:8: even with homogeneous equality, coercions
 will still be heterogeneous, and thus the need for a coherence coercion
 (of some form) will remain. The type of `~#` becomes homogeneous, but that
 affects only what coercions we can quantify over, not what ones we can
 form.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15192#comment:12>
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