[GHC] #12173: foldl' semantics changed from 4.7 to 4.8

[GHC]

#12173: foldl' semantics changed from 4.7 to 4.8
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        Reporter:  dfeuer            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Core Libraries    |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Runtime crash     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nomeata):

 I can confirm that this semantic change was accidental (I was picking this
 variant because it looks simpler). If the other one with `let` or `$!`
 fuses equally well, I’m all for changing it back and making it consistent.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12173#comment:3>
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