module System.Exit
    ( 
      ExitCode(ExitSuccess,ExitFailure)
    , exitWith      -- :: ExitCode -> IO a
    , exitFailure   -- :: IO a
  ) where

import Prelude

import Hugs.Prelude
import Hugs.Exception

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

-- | Computation 'exitWith' @code@ throws 'ExitException' @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
-- called 'exitFailure'.
-- A program that terminates successfully without calling 'exitWith'
-- explicitly is treated as it it had called 'exitWith' 'ExitSuccess'.
--
-- As an 'ExitException' 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 an 'Exception', 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'.

exitWith :: ExitCode -> IO a
exitWith ExitSuccess = throwIO (ExitException ExitSuccess)
exitWith code@(ExitFailure n)
  | n /= 0 = throwIO (ExitException code)

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