base-4.5.1.0: Basic libraries

Portabilityportable
Stabilityprovisional
Maintainer[email protected]
Safe HaskellTrustworthy

System.Exit

Description

Exiting the program.

Synopsis

Documentation

data ExitCode Source

Defines the exit codes that a program can return.

Constructors

ExitSuccess

indicates successful termination;

ExitFailure Int

indicates program failure with an exit code. The exact interpretation of the code is operating-system dependent. In particular, some values may be prohibited (e.g. 0 on a POSIX-compliant system).

exitWith :: ExitCode -> IO aSource

Computation exitWith code throws ExitCode code. Normally this terminates the program, returning code to the program's caller.

On program termination, the standard Handles stdout and stderr are flushed automatically; any other buffered Handles need to be flushed manually, otherwise the buffered data will be discarded.

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 ExitCode 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 a SomeException, and can be caught using the functions of Control.Exception. This means that cleanup computations added with 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.

exitFailure :: IO aSource

The computation exitFailure is equivalent to exitWith (ExitFailure exitfail), where exitfail is implementation-dependent.

exitSuccess :: IO aSource

The computation exitSuccess is equivalent to exitWith ExitSuccess, It terminates the program successfully.