{-# LANGUAGE Trustworthy #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  System.Exit
-- Copyright   :  (c) The University of Glasgow 2001
-- License     :  BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer  :  libraries@haskell.org
-- Stability   :  provisional
-- Portability :  portable
--
-- Exiting the program.
--
-----------------------------------------------------------------------------

module System.Exit
    (
      ExitCode(ExitSuccess,ExitFailure)
    , exitWith
    , exitFailure
    , exitSuccess
    , die
  ) where

import System.IO

import GHC.IO
import GHC.IO.Exception

-- ---------------------------------------------------------------------------
-- exitWith

-- | 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 'Control.Exception.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.
--
exitWith :: ExitCode -> IO a
exitWith :: forall a. ExitCode -> IO a
exitWith ExitCode
ExitSuccess = ExitCode -> IO a
forall e a. Exception e => e -> IO a
throwIO ExitCode
ExitSuccess
exitWith code :: ExitCode
code@(ExitFailure Int
n)
  | Int
n Int -> Int -> Bool
forall a. Eq a => a -> a -> Bool
/= Int
0 = ExitCode -> IO a
forall e a. Exception e => e -> IO a
throwIO ExitCode
code
  | Bool
otherwise = IOError -> IO a
forall a. IOError -> IO a
ioError (Maybe Handle
-> IOErrorType
-> String
-> String
-> Maybe CInt
-> Maybe String
-> IOError
IOError Maybe Handle
forall a. Maybe a
Nothing IOErrorType
InvalidArgument String
"exitWith" String
"ExitFailure 0" Maybe CInt
forall a. Maybe a
Nothing Maybe String
forall a. Maybe a
Nothing)

-- | The computation 'exitFailure' is equivalent to
-- 'exitWith' @(@'ExitFailure' /exitfail/@)@,
-- where /exitfail/ is implementation-dependent.
exitFailure :: IO a
exitFailure :: forall a. IO a
exitFailure = ExitCode -> IO a
forall a. ExitCode -> IO a
exitWith (Int -> ExitCode
ExitFailure Int
1)

-- | The computation 'exitSuccess' is equivalent to
-- 'exitWith' 'ExitSuccess', It terminates the program
-- successfully.
exitSuccess :: IO a
exitSuccess :: forall a. IO a
exitSuccess = ExitCode -> IO a
forall a. ExitCode -> IO a
exitWith ExitCode
ExitSuccess

-- | Write given error message to `stderr` and terminate with `exitFailure`.
--
-- @since 4.8.0.0
die :: String -> IO a
die :: forall a. String -> IO a
die String
err = Handle -> String -> IO ()
hPutStrLn Handle
stderr String
err IO () -> IO a -> IO a
forall a b. IO a -> IO b -> IO b
forall (m :: * -> *) a b. Monad m => m a -> m b -> m b
>> IO a
forall a. IO a
exitFailure