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diff --git a/GHC/TopHandler.lhs b/GHC/TopHandler.lhs
index 75d7b81..5fc3236 100644
--- a/GHC/TopHandler.lhs
+++ b/GHC/TopHandler.lhs
@@ -1,25 +1,21 @@
--- -----------------------------------------------------------------------------
--- $Id: TopHandler.lhs,v 1.6 2002/03/11 14:53:51 simonmar Exp $
---
--- (c) The University of Glasgow, 2001
+\begin{code}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  GHC.TopHandler
+-- Copyright   :  (c) The University of Glasgow, 2001-2002
+-- License     :  see libraries/base/LICENSE
+-- 
+-- Maintainer  :  cvs-ghc@haskell.org
+-- Stability   :  internal
+-- Portability :  non-portable (GHC Extensions)
 --
--- GHC.TopHandler
+-- Support for catching exceptions raised during top-level computations
+-- (e.g. @Main.main@, 'Control.Concurrent.forkIO', and foreign exports)
 --
--- 'Top-level' IO actions want to catch exceptions (e.g., forkIO and 
--- GHC.Main.mainIO) and report them - topHandler is the exception
--- handler they should use for this:
+-----------------------------------------------------------------------------
 
--- make sure we handle errors while reporting the error!
--- (e.g. evaluating the string passed to 'error' might generate
---  another error, etc.)
-
--- These functions can't go in GHC.Main, because GHC.Main isn't
--- included in HSstd.o (because GHC.Main depends on Main, which
--- doesn't exist yet...).
-
-\begin{code}
 module GHC.TopHandler (
-   runMain, reportStackOverflow, reportError 
+   runIO, runNonIO, reportStackOverflow, reportError 
   ) where
 
 import Prelude
@@ -30,22 +26,39 @@ import Foreign.C.String
 import Foreign.Ptr
 import GHC.IOBase
 import GHC.Exception
+import GHC.Prim (unsafeCoerce#)
 
--- runMain is applied to Main.main by TcModule
-runMain :: IO a -> IO ()
-runMain main = catchException (main >> return ()) topHandler
-  
-topHandler :: Exception -> IO ()
+-- | 'runIO' is wrapped around @Main.main@ by @TcModule@.  It is also wrapped
+-- around every @foreign export@ and @foreign import \"wrapper\"@ to mop up
+-- any uncaught exceptions.  Thus, the result of running
+-- 'System.Exit.exitWith' in a foreign-exported function is the same as
+-- in the main thread: it terminates the program.
+--
+runIO :: IO a -> IO a
+runIO main = catchException main topHandler
+
+-- | The same as 'runIO', but for non-IO computations.  Used for
+-- wrapping @foreign export@ and @foreign import \"wrapper\"@ when these
+-- are used to export Haskell functions with non-IO types.
+--
+runNonIO :: a -> IO a
+runNonIO a = catchException (a `seq` return a) topHandler
+
+topHandler :: Exception -> IO a
 topHandler err = catchException (real_handler err) topHandler
 
-real_handler :: Exception -> IO ()
+-- Make sure we handle errors while reporting the error!
+-- (e.g. evaluating the string passed to 'error' might generate
+--  another error, etc.)
+--
+real_handler :: Exception -> IO a
 real_handler ex =
   case ex of
 	AsyncException StackOverflow -> reportStackOverflow True
 
 	-- only the main thread gets ExitException exceptions
-	ExitException ExitSuccess     -> shutdownHaskellAndExit 0
-	ExitException (ExitFailure n) -> shutdownHaskellAndExit n
+	ExitException ExitSuccess     -> safe_exit 0
+	ExitException (ExitFailure n) -> safe_exit n
 
 	Deadlock    -> reportError True 
 			"no threads to run:  infinite loop or deadlock?"
@@ -53,28 +66,22 @@ real_handler ex =
 	ErrorCall s -> reportError True s
 	other       -> reportError True (showsPrec 0 other "\n")
 
--- NOTE: shutdownHaskellAndExit must be called "safe", because it *can*
--- re-enter Haskell land through finalizers.
-foreign import ccall "shutdownHaskellAndExit" 
-  shutdownHaskellAndExit :: Int -> IO ()
-
-reportStackOverflow :: Bool -> IO ()
+reportStackOverflow :: Bool -> IO a
 reportStackOverflow bombOut = do
    (hFlush stdout) `catchException` (\ _ -> return ())
    callStackOverflowHook
-   if bombOut then
-     stg_exit 2
-    else
-     return ()
+   if bombOut 
+	then exit 2
+	else return undefined
 
-reportError :: Bool -> String -> IO ()
+reportError :: Bool -> String -> IO a
 reportError bombOut str = do
    (hFlush stdout) `catchException` (\ _ -> return ())
    withCStringLen str $ \(cstr,len) -> do
      writeErrString errorHdrHook cstr len
      if bombOut 
-	then stg_exit 1
-        else return ()
+	then exit 1
+        else return undefined
 
 #ifndef ILX
 foreign import ccall "&ErrorHdrHook" errorHdrHook :: Ptr ()
@@ -92,4 +99,17 @@ foreign import ccall unsafe "stackOverflow"
 
 foreign import ccall unsafe "stg_exit"
 	stg_exit :: Int -> IO ()
+
+exit :: Int -> IO a
+exit r = unsafeCoerce# (stg_exit r)
+
+-- NOTE: shutdownHaskellAndExit must be called "safe", because it *can*
+-- re-enter Haskell land through finalizers.
+foreign import ccall "shutdownHaskellAndExit" 
+  shutdownHaskellAndExit :: Int -> IO ()
+
+-- we have to use unsafeCoerce# to get the 'IO a' result type, since the
+-- compiler doesn't let us declare that as the result type of a foreign export.
+safe_exit :: Int -> IO a
+safe_exit r = unsafeCoerce# (shutdownHaskellAndExit r)
 \end{code}