[GHC] #9356: scanl does not participate in stream fusion

[GHC]

#9356: scanl does not participate in stream fusion
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       Reporter:  dfeuer             |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler           |                 Version:  7.8.2
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:  Runtime
     Blocked By:                     |  performance bug
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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 nomeata came up with a fusing version of a strict `scanl'` in a comment on
 #9345. It's not entirely clear to me whether that's entirely safe, but a
 non-strict version of it for `scanl` would be, as both a good producer and
 good consumer, presumably made efficient using the same sorts of magic
 used in HEAD for `foldl`. The strict `scanl'` is obviously safe to write
 as a good consumer; only the production side remains to be proved.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9356>
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