runIO package:ghc-internal

The runIO function lets you run an I/O computation in the Q monad. Take care: you are guaranteed the ordering of calls to runIO within a single Q computation, but not about the order in which splices are run. Note: for various murky reasons, stdout and stderr handles are not necessarily flushed when the compiler finishes running, so you should flush them yourself.

runIO is wrapped around every foreign export and foreign import "wrapper" to mop up any uncaught exceptions. Thus, the result of running exitWith in a foreign-exported function is the same as in the main thread: it terminates the program.

Like runIO, but in the event of an exception that causes an exit, we don't shut down the system cleanly, we just exit. This is useful in some cases, because the safe exit version will give other threads a chance to clean up first, which might shut down the system in a different way. For example, try main = forkIO (runIO (exitWith (ExitFailure 1))) >> threadDelay 10000 This will sometimes exit with "interrupted" and code 0, because the main thread is given a chance to shut down when the child thread calls safeExit. There is a race to shut down between the main and child threads.

Input/output (dangerous). See runIO.