[GHC] #14266: AllowAmbiguousTypes doesn't play well with default class methods

[GHC]

#14266: AllowAmbiguousTypes doesn't play well with default class methods
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        Reporter:  chris-martin      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Its nothing to do with `AllowAmbiguousTypes`, except that the latter is
 needed to allow you to write the signature at all.  What I wrote all
 happens after the signature is accepted.

 > because DefaultSignatures emits code that doesn't use any instance
 signatures, right

 I don't understand that.  Your example made essential use of instance
 signatures.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14266#comment:14>
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