[GHC] #15349: fixST is a bit wrong

[GHC]

#15349: fixST is a bit wrong
-------------------------------------+-------------------------------------
        Reporter:  dfeuer            |                Owner:  dfeuer
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Core Libraries    |              Version:  8.5
      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:D4948
       Wiki Page:                    |
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Comment (by David Feuer <David.Feuer@…>):

 In [changeset:"5a49651f3161473b383ec497af38e9daa022b9ac/ghc"
 5a49651f/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="5a49651f3161473b383ec497af38e9daa022b9ac"
 Harden fixST

 Trac #15349 reveals that lazy blackholing can cause trouble for
 `fixST` much like it can for `fixIO`. Make `fixST` work just
 like `fixIO`.

 Reviewers: simonmar, hvr, bgamari

 Reviewed By: simonmar

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #15349

 Differential Revision: https://phabricator.haskell.org/D4948
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15349#comment:10>
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