System.Exit

base-4.11.1.0: Basic libraries

Copyright | (c) The University of Glasgow 2001
License | BSD-style (see the file libraries/base/LICENSE)
Maintainer | libraries@haskell.org
Stability | provisional
Portability | portable
Safe Haskell | Trustworthy
Language | Haskell2010

System.Exit

Description

Exiting the program.

Synopsis

- data ExitCode
  - = ExitSuccess
  - | ExitFailure Int
- exitWith :: ExitCode -> IO a
- exitFailure :: IO a
- exitSuccess :: IO a
- die :: String -> IO a

# Documentation

data ExitCode #

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).

Instances

Eq ExitCode # |
Instance details Defined in GHC.IO.Exception Methods (==) :: ExitCode -> ExitCode -> Bool Source # (/=) :: ExitCode -> ExitCode -> Bool Source #
Ord ExitCode # |
Instance details Defined in GHC.IO.Exception Methods compare :: ExitCode -> ExitCode -> Ordering Source # (<) :: ExitCode -> ExitCode -> Bool Source # (<=) :: ExitCode -> ExitCode -> Bool Source # (>) :: ExitCode -> ExitCode -> Bool Source # (>=) :: ExitCode -> ExitCode -> Bool Source # max :: ExitCode -> ExitCode -> ExitCode Source # min :: ExitCode -> ExitCode -> ExitCode Source #
Read ExitCode # |
Instance details Defined in GHC.IO.Exception Methods readsPrec :: Int -> ReadS ExitCode # readList :: ReadS [ExitCode] # readPrec :: ReadPrec ExitCode # readListPrec :: ReadPrec [ExitCode] #
Show ExitCode # |
Instance details Defined in GHC.IO.Exception Methods showsPrec :: Int -> ExitCode -> ShowS # show :: ExitCode -> String # showList :: [ExitCode] -> ShowS #
Generic ExitCode # |
Instance details Defined in GHC.IO.Exception Associated Types type Rep ExitCode :: * -> * # Methods from :: ExitCode -> Rep ExitCode x # to :: Rep ExitCode x -> ExitCode #
Exception ExitCode # | Since: base-4.1.0.0
Instance details Defined in GHC.IO.Exception Methods toException :: ExitCode -> SomeException # fromException :: SomeException -> Maybe ExitCode # displayException :: ExitCode -> String #
type Rep ExitCode # |
Instance details Defined in GHC.IO.Exception type Rep ExitCode = D1 (MetaData "ExitCode" "GHC.IO.Exception" "base" False) (C1 (MetaCons "ExitSuccess" PrefixI False) (U1 :: * -> *) :+: C1 (MetaCons "ExitFailure" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 Int)))

exitWith :: ExitCode -> IO a #

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

On program termination, the standard `Handle`s `stdout` and `stderr` are flushed automatically; any other buffered `Handle`s 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 if 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 a #

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

exitSuccess :: IO a #

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

die :: String -> IO a #

Write given error message to `stderr` and terminate with `exitFailure`.

Since: base-4.8.0.0