[GHC] #9345: Data.List.inits is extremely slow

[GHC]

#9345: Data.List.inits is extremely slow
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              Reporter:  dfeuer      |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:  7.8.4
             Component:              |          Version:  7.8.3
  libraries/base                     |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:  Runtime     |       Blocked By:
  performance bug                    |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by nomeata):

 > I was finally able to figure out how to read that file, and wow. Those
 are some impressive results.

 Of course the allocation and destruction of the `Queue` is not for free.
 Just to make sure I didn’t do anything stupid: Can you reproduce my
 results?

 If we are worried about `seq` we can simply inline my `myScanl'` in
 `initsQ2` and replace the `seq` by `case` statements. Or leave the `seq`
 but argue that we are always applying them to values of type `Queue`,
 nothing breaks. And by that argument, as long as `myScanl` is only used
 for `initsQ2`, we should be safe.

 I guess we only should worry about actually adding `scanl'` to the
 libraries, but that’s a different issue and should be discussed in #9356 I
 guess.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9345#comment:13>
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