[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 chris-martin):

 Thanks Ryan - yes that's a great description of what I was trying to do.
 One correction: I'm pretty sure `MultiMonoid` alone ''does'' require
 `AllowAmbiguousTypes` even before you get to `MultiFoldable`.

 The "complete" result is now on Hackage

 https://hackage.haskell.org/package/multi-
 instance-0.0.0.1/docs/MultiInstance.html

 although I ended up scrapping the `MultiFoldable` class altogether.

 It was an extended thought experiment more than anything, probably beyond
 the bounds of reasonable Haskell.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14266#comment:5>
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