-----------------------------------------------------------------------------
module System.Exit
- (
+ (
ExitCode(ExitSuccess,ExitFailure)
, exitWith -- :: ExitCode -> IO a
, exitFailure -- :: IO a
+ , exitSuccess -- :: IO a
) where
import Prelude
#ifdef __GLASGOW_HASKELL__
-import GHC.IOBase
+import GHC.IO
+import GHC.IO.Exception
#endif
#ifdef __HUGS__
-import Hugs.Prelude
+import Hugs.Prelude (ExitCode(..))
+import Control.Exception.Base
#endif
#ifdef __NHC__
-- ---------------------------------------------------------------------------
-- exitWith
--- `exitWith code' terminates the program, returning `code' to the
--- program's caller. Before it terminates, any open or semi-closed
--- handles are first closed.
-
+-- | 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
+-- 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.
+--
#ifndef __NHC__
exitWith :: ExitCode -> IO a
-exitWith ExitSuccess = throw (ExitException ExitSuccess)
+exitWith ExitSuccess = throwIO ExitSuccess
exitWith code@(ExitFailure n)
- | n /= 0 = throw (ExitException code)
+ | n /= 0 = throwIO code
#ifdef __GLASGOW_HASKELL__
- | otherwise = ioError (IOError Nothing InvalidArgument "exitWith" "ExitFailure 0" Nothing)
+ | otherwise = ioError (IOError Nothing InvalidArgument "exitWith" "ExitFailure 0" Nothing Nothing)
#endif
#endif /* ! __NHC__ */
+-- | 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
+-- sucessfully.
+exitSuccess :: IO a
+exitSuccess = exitWith ExitSuccess