1 -----------------------------------------------------------------------------
3 -- Module : System.Exit
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/base/LICENSE)
7 -- Maintainer : libraries@haskell.org
8 -- Stability : provisional
9 -- Portability : portable
11 -- Exiting the program.
13 -----------------------------------------------------------------------------
17 ExitCode(ExitSuccess,ExitFailure)
18 , exitWith -- :: ExitCode -> IO a
19 , exitFailure -- :: IO a
20 , exitSuccess -- :: IO a
25 #ifdef __GLASGOW_HASKELL__
27 import GHC.IO.Exception
31 import Hugs.Prelude (ExitCode(..))
32 import Control.Exception.Base
42 -- ---------------------------------------------------------------------------
45 -- | Computation 'exitWith' @code@ throws 'ExitCode' @code@.
46 -- Normally this terminates the program, returning @code@ to the
49 -- On program termination, the standard 'Handle's 'stdout' and
50 -- 'stderr' are flushed automatically; any other buffered 'Handle's
51 -- need to be flushed manually, otherwise the buffered data will be
54 -- A program that fails in any other way is treated as if it had
55 -- called 'exitFailure'.
56 -- A program that terminates successfully without calling 'exitWith'
57 -- explicitly is treated as it it had called 'exitWith' 'ExitSuccess'.
59 -- As an 'ExitCode' is not an 'IOError', 'exitWith' bypasses
60 -- the error handling in the 'IO' monad and cannot be intercepted by
61 -- 'catch' from the "Prelude". However it is a 'SomeException', and can
62 -- be caught using the functions of "Control.Exception". This means
63 -- that cleanup computations added with 'Control.Exception.bracket'
64 -- (from "Control.Exception") are also executed properly on 'exitWith'.
66 -- Note: in GHC, 'exitWith' should be called from the main program
67 -- thread in order to exit the process. When called from another
68 -- thread, 'exitWith' will throw an 'ExitException' as normal, but the
69 -- exception will not cause the process itself to exit.
72 exitWith :: ExitCode -> IO a
73 exitWith ExitSuccess = throwIO ExitSuccess
74 exitWith code@(ExitFailure n)
75 | n /= 0 = throwIO code
76 #ifdef __GLASGOW_HASKELL__
77 | otherwise = ioError (IOError Nothing InvalidArgument "exitWith" "ExitFailure 0" Nothing Nothing)
79 #endif /* ! __NHC__ */
81 -- | The computation 'exitFailure' is equivalent to
82 -- 'exitWith' @(@'ExitFailure' /exitfail/@)@,
83 -- where /exitfail/ is implementation-dependent.
85 exitFailure = exitWith (ExitFailure 1)
87 -- | The computation 'exitSuccess' is equivalent to
88 -- 'exitWith' 'ExitSuccess', It terminates the program
91 exitSuccess = exitWith ExitSuccess