[GHC] #8994: type checker could not deduce ambiguous instances

[GHC]

#8994: type checker could not deduce ambiguous instances
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        Reporter:  divip             |            Owner:
            Type:  bug               |           Status:  closed
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.8.2
      Resolution:  invalid           |         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 divip):

 Thanks for the explanation.

 About my user experience:
 The example code was extracted from a bigger program.
 I did incremental refactoring steps on my program. In one step I
 introduced a new associated type which was independent of the rest of the
 program (like `type F a` above which should not interfere with
 defaulting), and my program stopped to compile.
 So I was almost sure this is a compiler bug.

 Improving on this behaviour is not very important for me, it was just
 unexpected during programming.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8994#comment:3>
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