add GHC.HetMet.{hetmet_kappa,hetmet_kappa_app}

[ghc-base.git] / System / Exit.hs

diff --git a/System/Exit.hs b/System/Exit.hs
index 3c2aea2..7eb17cf 100644 (file)
--- a/System/Exit.hs
+++ b/System/Exit.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  System.Exit
@@ -13,20 +15,23 @@
 -----------------------------------------------------------------------------
 
 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__
@@ -39,19 +44,50 @@ import System
 -- ---------------------------------------------------------------------------
 -- 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.
+--
+-- 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.
+--
 #ifndef __NHC__
 exitWith :: ExitCode -> IO a
-exitWith ExitSuccess = throwIO (ExitException ExitSuccess)
+exitWith ExitSuccess = throwIO ExitSuccess
 exitWith code@(ExitFailure n)
-  | n /= 0 = throwIO (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
+-- successfully.
+exitSuccess :: IO a
+exitSuccess = exitWith ExitSuccess