[GHC] #16406: Array code works with GHC 8.4.4, hangs with GHC 8.6.4

[GHC]

#16406: Array code works with GHC 8.4.4, hangs with GHC 8.6.4
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        Reporter:  arybczak          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  libraries         |              Version:  8.6.4
  (other)                            |
      Resolution:                    |             Keywords:  array
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dfeuer):

 That was an intentional change. As I recall: Haskell 98's reference
 implementation didn't match its spec. We followed the Result: `accumArray`
 was terribly inefficient. Is there real code in the wild that makes use of
 its former laziness?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16406#comment:7>
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