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import Posix
import System(ExitCode(..), exitWith)
main =
forkProcess >>= \ maybe_pid ->
case maybe_pid of
Nothing -> raiseSignal floatingPointException
_ -> doParent
doParent =
getAnyProcessStatus True False >>= \ (Just (pid, tc)) ->
case tc of
Terminated sig | sig == floatingPointException -> forkChild2
_ -> fail (userError "unexpected termination cause")
forkChild2 =
forkProcess >>= \ maybe_pid ->
case maybe_pid of
Nothing -> exitImmediately (ExitFailure 42)
_ -> doParent2
doParent2 =
getAnyProcessStatus True False >>= \ (Just (pid, tc)) ->
case tc of
Exited (ExitFailure 42) -> forkChild3
_ -> fail (userError "unexpected termination cause (2)")
forkChild3 =
forkProcess >>= \ maybe_pid ->
case maybe_pid of
Nothing -> exitImmediately (ExitSuccess)
_ -> doParent3
doParent3 =
getAnyProcessStatus True False >>= \ (Just (pid, tc)) ->
case tc of
Exited ExitSuccess -> forkChild4
_ -> fail (userError "unexpected termination cause (3)")
forkChild4 =
forkProcess >>= \ maybe_pid ->
case maybe_pid of
Nothing -> raiseSignal softwareStop
_ -> doParent4
doParent4 =
getAnyProcessStatus True True >>= \ (Just (pid, tc)) ->
case tc of
Stopped sig | sig == softwareStop -> enoughAlready pid
_ -> fail (userError "unexpected termination cause (4)")
enoughAlready pid =
signalProcess killProcess pid >>
getAnyProcessStatus True True >>= \ (Just (pid, tc)) ->
case tc of
Terminated sig | sig == killProcess -> putStr "I'm happy.\n"
_ -> fail (userError "unexpected termination cause (5)")
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