[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):

 I agree with Stephanie's first few paragraphs, but not her last one. GHC
 ''already'' works up to erasure-equivalence. That is, `eqType` returns
 `True` whenever two types are erasure-equivalent (and have the same
 kinds). But we still need the coherence coercions, because they sometimes
 change kinds.

 I guess that will change once we move to homogeneous equality, though...

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15192#comment:8>
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