[GHC] #11099: Incorrect warning about redundant constraints

[GHC]

#11099: Incorrect warning about redundant constraints
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        Reporter:  diatchki          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.11
  checker)                           |
      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):

 * You want to give a signature to the function that is less polymorphic
 than its most general type.
 * You may have legitimate reasons for wanting to do so.
 * Insofar as you do so by adding a constraint that isn't used, GHC may
 complain if you use `-fwarn-redundant-constraints`.

 Hmm.  We'd really like a per-function way of suppressing the warning.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11099#comment:4>
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