[GHC] #11760: runST with lazy blackholing breaks referential transparency

[GHC]

#11760: runST with lazy blackholing breaks referential transparency
-------------------------------------+-------------------------------------
        Reporter:  Yuras             |                Owner:  dfeuer
            Type:  bug               |               Status:  patch
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Core Libraries    |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3038
       Wiki Page:                    |
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Comment (by David Feuer <David.Feuer@…>):

 In [changeset:"2f5cb3d44d05e581b75a47fec222577dfa7a533e/ghc"
 2f5cb3d4/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="2f5cb3d44d05e581b75a47fec222577dfa7a533e"
 Attempt to make lazy ST thread safe

 Use `noDuplicate#` to prevent lazy `ST` thunks from
 being evaluated in multiple GHC threads.

 Some lazy `ST` functions added laziness that did not seem to be useful
 (e.g.,
 creating lazy pairs that will never be matched unless one of their
 components
 is demanded). Stripped that out.

 Reviewers: ekmett, simonpj, bgamari, simonmar, austin, hvr

 Subscribers: rwbarton, thomie

 Differential Revision: https://phabricator.haskell.org/D3038

 GHC Trac Issues: #11760
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11760#comment:15>
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