Computation exitWith code throws ExitException code. Normally this terminates the program, returning code to the program's caller. Before the program terminates, any open or semi-closed handles are first closed.

A program that fails in any other way is treated as if it had called exitFailure. A program that terminates successfully without calling exitWith explicitly is treated as it it had called exitWith ExitSuccess.

As an ExitException is not an IOError, exitWith bypasses the error handling in the IO monad and cannot be intercepted by catch from the Prelude. However it is an Exception, and can be caught using the functions of Control.Exception. This means that cleanup computations added with Control.Exception.bracket (from Control.Exception) are also executed properly on exitWith.

Note: in GHC, exitWith should be called from the main program thread in order to exit the process. When called from another thread, exitWith will throw an ExitException as normal, but the exception will not cause the process itself to exit.