[GHC] #9398: Data.List.cycle is not a good producer

[GHC]

#9398: Data.List.cycle is not a good producer
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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):

 Staring at this case a bit more, I conclude that we will never get good
 code from fusing a higher order foldr (like `foldl` or `take` or anything
 with an accumulating parameter) with a cyclic producer. It will
 sucessfully tie the know, but a knot of type `Int# -> Int` (and we can see
 this happening here). So it will create 5 function closures of that type
 that call each other in a round-robin style; the pattern match on the list
 elements happens only once.

 And I as there is no way to pull the accumulating argument into the knot
 (after all, it changes while going round the circle), this can hardly be
 avoided.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9398#comment:20>
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