[GHC] #10778: GHC doesn't infer all constrains

[GHC]

#10778: GHC doesn't infer all constrains
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        Reporter:  danilo2           |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by danilo2):

 No, But there are the GADTs constraints:
 {{{
 IndexOf a cont ~ idx, ElementByIdx idx cont ~ a, Measurable cont
 }}}
 So {{{idx}}} is always result of {{{IndexOf a cont}}}. Is this information
 not enough for Haskell?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10778#comment:4>
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