[GHC] #3397: :step hangs when -fbreak-on-exception is set

[GHC]

#3397: :step hangs when -fbreak-on-exception is set
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        Reporter:  hamish            |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:  7.2.1
       Component:  GHCi              |                 Version:  7.10.1-rc2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:  x86
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Changes (by gelisam):

 * cc: hvr (added)
 * status:  closed => new
 * version:  6.10.3 => 7.10.1-rc2
 * resolution:  worksforme =>


Comment:

 I have encountered this very old bug with GHC 7.10.0.20150123, here's a
 minimal test case:

 {{{#!hs
 mapLookup :: () -> ()
 mapLookup = go
   where
     go () = ()

 withDummyLookup :: IO a -> IO a
 withDummyLookup body = do
     mapLookup () `seq` return ()
     body

 main :: IO ()
 main = withDummyLookup (return ())
 }}}

 To reproduce:

 {{{
 $ ghci Example.hs
 *Main> :set -fbreak-on-exception
 *Main> :steplocal main
 Stopped at Example.hs:12:8-34
 _result :: IO () = _
 [Example.hs:12:8-34] *Main> :steplocal
 (hangs forever)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3397#comment:6>
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