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

3 Oct 2017

      #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 RyanGlScott):

 I'm a bit lost here. Your "reduced" example seems to be asking a lot more
 out of GHC than what the original example demands! That is, the original
 example is simply:

 {{{#!hs
 class A t where
   f :: forall x m. Monoid x => t m -> m

 instance A [] where
   f :: forall x m. Monoid x => [m] -> m
   f = blah
 }}}

 No superclass relationships. No argument swizzling. I'd be content with
 just this, since that's all that `DefaultSignatures` needs! Does that make
 the problem easier?

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14266#comment:11
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