[GHC] #9949: zipWith too strict in second argument in GHC-7.10.0

[GHC]

#9949: zipWith too strict in second argument in GHC-7.10.0
-------------------------------------+-------------------------------------
        Reporter:  Lemming           |                   Owner:  ekmett
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  libraries/base    |                 Version:  7.10.1-rc1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by Lemming):

 I found the difference because my `mapAdjacent` function uses `tail` in
 the second argument of `zipWith`:
 {{{
 mapAdjacent :: (a -> a -> b) -> [a] -> [b]
 mapAdjacent f xs = zipWith f xs (tail xs)
 }}}

 I get:
 {{{
 $ ghci-7.10.0.20141227
 *Prelude> Data.List.HT.mapAdjacent (==) ([] :: [Int])
 *** Exception: Prelude.tail: empty list
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9949#comment:4>
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