[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 simonpj):

 OK, so I think at least part of this ticket has a conclusion:

  * We should try newtype unwrapping before trying decomposition.  (But
 please let's try identity first of all in case the two types are
 identical.)

  * The reason for this ordering should be captured in a `Note`

  * I think it would also be highly worthwhile to start a new "user-
 documentation" page on the Haskell wiki, linked from
 [http://www.haskell.org/haskellwiki/GHC/Type_system GHC type system
 extensions].  This gives a user-updatable place to explain how to use the
 raw facilities.  The points explained above in comments 11-14 are far from
 obvious, and it'd be great to have them articulated there.

 Joachim might you do these things?   Thanks.

 That still leaves the original topic of the ticket (decomposing
 applications) open.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9117#comment:15>
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