Re: [GHC] #13615: Nondeterminism in ‘pure’ function w/ parallel evaluation & memo combinators

[GHC]

#13615: Nondeterminism in ‘pure’ function w/ parallel evaluation & memo combinators
-------------------------------------+-------------------------------------
        Reporter:  pacak             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.2.1-rc2
      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):
       Wiki Page:                    |
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Comment (by pacak):

 {{{
 <bgamari> gamebooksolver-solvebook02: Those are expected to be
 equal(6030,6030)
 <bgamari> GHC has an interesting sense of equality
 }}}

 Code that generates this error looks like this and both `s'` and `s` are
 `Int`s.

 {{{
       if s' /= s
             then error $ "Those are expected to be equal" ++ show (s', s)
             else xs'
 }}}

 I don't see how that's possible unless `Eq` instance for `Int` gets
 corrupted somehow. If that's the case - it also might mean `Num` instance
 is bogus as well and that results in wrong sum.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13615#comment:15>
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