|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).
|Computation getArgs returns a list of the program's command
line arguments (not including the program name).
Computation getProgName returns the name of the program as it was
However, this is hard-to-impossible to implement on some non-Unix
OSes, so instead, for maximum portability, we just return the leafname
of the program as invoked. Even then there are some differences
between platforms: on Windows, for example, a program invoked as foo
is probably really FOO.EXE, and that is what getProgName will return.
Computation getEnv var returns the value
of the environment variable var.
This computation may fail with:
- System.IO.Error.isDoesNotExistError if the environment variable
does not exist.
Computation system cmd returns the exit code produced when the
operating system runs the shell command cmd.
This computation may fail with
- PermissionDenied: The process has insufficient privileges to
perform the operation.
- ResourceExhausted: Insufficient resources are available to
perform the operation.
- UnsupportedOperation: The implementation does not support
On Windows, system passes the command to the Windows command
interpreter (CMD.EXE or COMMAND.COM), hence Unixy shell tricks
will not work.
Computation exitWith code throws ExitCode 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
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 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.
|The computation exitFailure is equivalent to
exitWith (ExitFailure exitfail),
where exitfail is implementation-dependent.
|Produced by Haddock version 2.6.1|