[GHC] #9537: concatMap is not a good producer for list fusion (was: concatMap does not participate in list fusion)

[GHC]

#9537: concatMap is not a good producer for list fusion
-------------------------------------+-------------------------------------
              Reporter:  dfeuer      |            Owner:  ekmett
                  Type:  bug         |           Status:  patch
              Priority:  normal      |        Milestone:  7.10.1
             Component:  Core        |          Version:  7.9
  Libraries                          |         Keywords:  fusion
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:  Runtime     |  Related Tickets:
  performance bug                    |
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D348   |
-------------------------------------+-------------------------------------
Changes (by dfeuer):

 * cc: core-libraries-committee@… (added)
 * status:  new => patch
 * differential:   => Phab:D348


Old description:

> Joachim Breitner raised this issue in an
> [http://www.haskell.org/pipermail/haskell-cafe/2011-December/097228.html
> email to haskell-cafe] in 2011, but he never got a response. For some
> reason, list comprehensions desugar to `concatMap` forms written to fuse,
> but the actual `concatMap` function is not written so. Unless there is a
> good reason for this, we should make it fuse.

New description:

 Joachim Breitner raised this issue in an [http://www.haskell.org/pipermail
 /haskell-cafe/2011-December/097228.html email to haskell-cafe] in 2011,
 but he never got a response. For some reason, list comprehensions desugar
 to `concatMap` forms written to fuse fully, but the actual `concatMap`
 function is not written so. Unless there is a good reason for this, we
 should make it fuse better.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9537#comment:3>
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