[project @ 2002-08-30 14:19:18 by simonpj]

[ghc-base.git] / GHC / Exception.lhs

diff --git a/GHC/Exception.lhs b/GHC/Exception.lhs
index abf9a82..5822ea8 100644 (file)
--- a/GHC/Exception.lhs
+++ b/GHC/Exception.lhs
@@ -1,13 +1,18 @@
-% ------------------------------------------------------------------------------
-% $Id: Exception.lhs,v 1.1 2001/06/28 14:15:03 simonmar Exp $
-%
-% (c) The University of Glasgow, 1998-2000
-%
-
-Exceptions and exception-handling functions.
-
 \begin{code}
 {-# OPTIONS -fno-implicit-prelude #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  GHC.Exception
+-- Copyright   :  (c) The University of Glasgow, 1998-2002
+-- License     :  see libraries/base/LICENSE
+-- 
+-- Maintainer  :  cvs-ghc@haskell.org
+-- Stability   :  internal
+-- Portability :  non-portable (GHC extensions)
+--
+-- Exceptions and exception-handling functions.
+-- 
+-----------------------------------------------------------------------------
 
 #ifndef __HUGS__
 module GHC.Exception 
@@ -17,8 +22,9 @@ module GHC.Exception
          throw, ioError ) 
   where
 
+import Data.Either
+
 import GHC.Base
-import GHC.Maybe
 import GHC.IOBase
 
 #endif
@@ -53,7 +59,6 @@ catchException (IO m) k =  IO $ \s -> catch# m (\ex -> unIO (k ex)) s
 catch           :: IO a -> (Exception -> IO a) -> IO a 
 catch m k      =  catchException m handler
   where handler err@(IOException _) = k err
-        handler err@(UserError   _) = k err
        handler other               = throw other
 \end{code}
 
@@ -104,17 +109,27 @@ bracket_ before after m = do
 %*********************************************************
 
 \begin{code}
-#ifndef __HUGS__
+-- | Applying 'block' to a computation will
+-- execute that computation with asynchronous exceptions
+-- /blocked/.  That is, any thread which
+-- attempts to raise an exception in the current thread will be
+-- blocked until asynchronous exceptions are enabled again.  There\'s
+-- no need to worry about re-enabling asynchronous exceptions; that is
+-- done automatically on exiting the scope of
+-- 'block'.
 block :: IO a -> IO a
-block (IO io) = IO $ blockAsyncExceptions# io
 
+-- | To re-enable asynchronous exceptions inside the scope of
+-- 'block', 'unblock' can be
+-- used.  It scopes in exactly the same way, so on exit from
+-- 'unblock' asynchronous exception delivery will
+-- be disabled again.
 unblock :: IO a -> IO a
+
+#ifndef __HUGS__
+block (IO io) = IO $ blockAsyncExceptions# io
 unblock (IO io) = IO $ unblockAsyncExceptions# io
 #else
--- Not implemented yet in Hugs.
-block :: IO a -> IO a
-block (IO io) = IO io
-
 unblock :: IO a -> IO a
 unblock (IO io) = IO io
 #endif