[GHC] #12133: ConstraintKinds inference failure (regression from 7.10)

[GHC]

#12133: ConstraintKinds inference failure (regression from 7.10)
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        Reporter:  goldfire      |                Owner:
            Type:  bug           |               Status:  new
        Priority:  normal        |            Milestone:  8.0.2
       Component:  Compiler      |              Version:  8.0.1
      Resolution:                |             Keywords:
Operating System:  Linux         |         Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown  |            Test Case:
      Blocked By:                |             Blocking:
 Related Tickets:                |  Differential Rev(s):
       Wiki Page:                |
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Changes (by simonpj):

 * milestone:   => 8.0.2


Comment:

 I think this is another manifestation of some bugs in my implementation of
 recursive superclasses, which was in 8.0.  Happily it works just fine in
 HEAD.

 The commit that that may have fixed it is (see #12175)
 {{{
 commit ce97b7298d54bdfccd9dcf366a69c5617b4eb43f
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Wed Jun 22 14:17:58 2016 +0100

     Expand given superclasses more eagerly
 }}}
 but I have not tested this.

 I'm not sure how vigorously we should try to get a fix into 8.0.2, but
 I'll milestone it as such.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12133#comment:3>
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