[GHC] #9258: Type inference fails with closed type families

[GHC]

#9258: Type inference fails with closed type families
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        Reporter:  augustss          |            Owner:
            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 augustss):

 I don't see why ghc couldn't infer the commented out type.  In a similar
 example
 {{{
 --f :: D d Double ~ Double => Descr d -> Double
 f d = fld d :: Double
 }}}
 ghc is able to infer the commented out type.

 (Of course, for this function an error message would have been appropriate
 since there is no way this function can ever be used; it's like having
 Bool~Double as a constraint.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9258#comment:2>
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