[GHC] #12142: -Wredundant-constraints warns about constraints introduced via type synonyms.

[GHC]

#12142: -Wredundant-constraints warns about constraints introduced via type
synonyms.
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        Reporter:  scshunt           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 I can see that's annoying, but it's hard to avoid.  And it does tell you
 something useful, namely that `l` is less polymorphic, and therefore less
 usable, than it could be.

 It's tantalising -- `-Wredundant-constraints` really is jolly useful but
 it is also sometimes annoying.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12142#comment:1>
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