[GHC] #8423: contraint solver doesn't reduce reducible closed type family expressions (even with undecidable instances!)

[GHC]

#8423: contraint solver doesn't  reduce reducible closed type family expressions
(even with undecidable instances!)
--------------------------------------------+------------------------------
        Reporter:  carter                   |            Owner:
            Type:  feature request          |           Status:  new
        Priority:  normal                   |        Milestone:  7.10.1
       Component:  Compiler (Type checker)  |          Version:  7.7
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  None/Unknown             |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
--------------------------------------------+------------------------------
Changes (by carter):

 * type:  bug => feature request
 * milestone:  7.8.1 => 7.10.1


Comment:

 Though I imagine theres some subtleties to adding such machinery, but it
 might be a great way to allow more "proofs by computation" to work out in
 Haskell

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8423#comment:2>
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