[GHC] #3680: Improve docs for 'length'

[GHC]

#3680: Improve docs for 'length'
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    Reporter:  daniel.is.fischer  |       Owner:                   
        Type:  feature request    |      Status:  new              
    Priority:  normal             |   Component:  libraries/base   
     Version:  6.10.4             |    Keywords:                   
          Os:  Unknown/Multiple   |    Testcase:                   
Architecture:  Unknown/Multiple   |     Failure:  Documentation bug
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 The haddock docs for 'length' and 'genericLength' give no indication of
 their complexity. This leads to many inadvertent uses of 'length', causing
 poor performance.

 To reduce the number of those cases, I suggest inserting the complexity
 (/O(n)/) into the haddock docs, perhaps even a warning to the effect of
 "use only if you really want to know the length".

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3680>
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