content: {-# 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 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.
  --
  exitWith :: ExitCode -> IO a
  exitWith ExitSuccess = throwIO ExitSuccess
  exitWith code@(ExitFailure n)
    | n /= 0 = throwIO code
    | otherwise = ioError (IOError Nothing InvalidArgument "exitWith" "ExitFailure 0" Nothing Nothing)
  
  -- | The computation 'exitFailure' is equivalent to
  -- 'exitWith' @(@'ExitFailure' /exitfail/@)@,
  -- where /exitfail/ is implementation-dependent.
  exitFailure :: IO a
  exitFailure = exitWith (ExitFailure 1)
  
  -- | The computation 'exitSuccess' is equivalent to
  -- 'exitWith' 'ExitSuccess', It terminates the program
  -- successfully.
  exitSuccess :: IO a
  exitSuccess = exitWith ExitSuccess
  
  -- | Write given error message to `stderr` and terminate with `exitFailure`.
  --
  -- @since 4.8.0.0
  die :: String -> IO a
  die err = hPutStrLn stderr err >> exitFailure
  