[GHC] #13593: Unexpected behavior from Data.List.groupBy

[GHC]

#13593: Unexpected behavior from Data.List.groupBy
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        Reporter:  dsf               |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Core Libraries    |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Documentation     |  Unknown/Multiple
  bug                                |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dsf):

 Replying to [comment:12 svenpanne]:
 > Hmmm, does that mean that every single function under 'The "By"
 operations' will get the sentence 'The predicate is assumed to define an
 equivalence.' '/ The function is assumed to define a total ordering.'?
 It's a little bit like repeating similar sentences for every function
 taking an Eq/Ord context...

 Definitely not - this is a recipe for teaching people to ignore stuff.
 Elsewhere I said it makes sense to put it in the header, but consider that
 the particularly unexpected results come from groupBy.  In the other cases
 you probablyu wouldn't consider using a non-transitive function argument:

 {{{#!hs
 -- What do these mean?
 > nubBy notBoth1 [1,1,2,3,1,1,4,5,6,1]
 [1,1,1,1,1]
 > deleteBy notBoth1 3 [1,1,2,3,1,1,4,5,6,1]
 [1,2,3,1,1,4,5,6,1]
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13593#comment:14>
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