[GHC] #9117: Coercible constraint solver misses one

[GHC]

#9117: Coercible constraint solver misses one
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        Reporter:  goldfire          |            Owner:  nomeata
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.8.2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by goldfire):

 Fair enough. I believe any of these problems exist with non-pathologically
 recursive newtypes, such as my `Bar` example in comment:21. But, I'm also
 happy enough to say "caveat programmer" if they use recursive newtypes
 with `Coercible`. We should make sure to say that somewhere, though.

 If we neglect recursive newtypes (which is reasonable, I would say) then
 the reordered solver (as it is in HEAD, as I understand) seems better than
 the one released with 7.8.2. But, how are we faring on the original
 request at the top?

 PS: Just realized that I never contributed to the wiki page. Will do
 shortly.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9117#comment:27>
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