[GHC] #11762: GHC 8 superclass chain constraint regression

[GHC]

#11762: GHC 8 superclass chain constraint regression
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        Reporter:  _deepfire         |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc2
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11427            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Yes, it's the same as #11427.

 It doesn't bite often, and it's also easy to fix, thus
 {{{
 instance (Super a, Left a) ⇒ Right a
 }}}
 What I most dislike about it is that it's hard to explain and justify.  I
 would like a better way to do this, but I don't know one.  Better ideas
 welcome!

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11762#comment:5>
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