[GHC] #11555: catch _|_ breaks at -O1

[GHC]

#11555: catch _|_ breaks at -O1
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        Reporter:  slyfox            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.0.1-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 NeilMitchell):

 I have tried the two suggestions for "lazy catch", namely:

 {{{#!hs
 safeCatch1 a b = join (evaluate a) `catch` b
 safeCatch2 a b = lazy a `catch` b
 }}}

 Both work in isolation on the tiny example. Only {{{safeCatch1}}} works in
 the Shake test suite, with {{{safeCatch2}}} I get the same error as
 before. That suggests that {{{lazy}}} is somehow insufficient to obtain
 the original behaviour.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11555#comment:12>
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