[project @ 2005-03-09 17:47:50 by simonpj]

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

diff --git a/System/Exit.hs b/System/Exit.hs
index db37a7f..1dab14f 100644 (file)
--- a/System/Exit.hs
+++ b/System/Exit.hs
@@ -26,23 +26,49 @@ import GHC.IOBase
 #endif
 
 #ifdef __HUGS__
-import Hugs.System
+import Hugs.Prelude
+import Hugs.Exception
+#endif
+
+#ifdef __NHC__
+import System
+  ( ExitCode(..)
+  , exitWith
+  )
 #endif
 
 -- ---------------------------------------------------------------------------
 -- 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 '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'.
 
-#ifdef __GLASGOW_HASKELL__
+#ifndef __NHC__
 exitWith :: ExitCode -> IO a
-exitWith ExitSuccess = throw (ExitException ExitSuccess)
-exitWith code@(ExitFailure n) 
-  | n == 0 = ioException (IOError Nothing InvalidArgument "exitWith" "ExitFailure 0" Nothing)
-  | otherwise = throw (ExitException code)
-#endif  /* __GLASGOW_HASKELL__ */
+exitWith ExitSuccess = throwIO (ExitException ExitSuccess)
+exitWith code@(ExitFailure n)
+  | n /= 0 = throwIO (ExitException code)
+#ifdef __GLASGOW_HASKELL__
+  | otherwise = ioError (IOError Nothing InvalidArgument "exitWith" "ExitFailure 0" 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)