[GHC] #11715: Constraint vs *

[GHC]

#11715: Constraint vs *
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        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |
      Resolution:                    |             Keywords:  Typeable
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 goldfire):

 Hm. Perhaps you're right that my suggestion goes against the spirit of
 Haskell constraints and that it would be more sensible to simply rename
 `with` to `incoherentWith`. Instead of my proposed error, we could simply
 add a warning when GHC detects (on a best effort basis) an ambiguous
 constraint. This warning would be triggered in `cmp`, for example, and
 silly uses of `incoherentWith`. Or perhaps not in `cmp` because GHC can
 detect that the ambiguously satisfied constraint is actually a class
 constraint and therefore assumed to be coherent.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11715#comment:27>
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