X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Futils%2FException.hs;h=3c7600515a13abc68950bf74c3730b17db71edd1;hb=4fa44a3ae9c36222ccb460ba3ed24e46bf7c70ae;hp=8d5d4389b6ca525c4b5e4f5d0b375d88d6aec735;hpb=4767e535d9761920a18629a4142d3a929503b936;p=ghc-hetmet.git

diff --git a/compiler/utils/Exception.hs b/compiler/utils/Exception.hs
index 8d5d438..3c76005 100644
--- a/compiler/utils/Exception.hs
+++ b/compiler/utils/Exception.hs
@@ -7,56 +7,45 @@ module Exception
     where
 
 import Prelude hiding (catch)
-import Control.Exception
 
 #if __GLASGOW_HASKELL__ < 609
-import Data.Typeable ( Typeable )
-
-type SomeException = Exception
-
-onException :: IO a -> IO () -> IO a
-onException io what = io `catch` \e -> do what
-                                          throw e
+import Control.Exception.Extensible as Control.Exception
+#else
+import Control.Exception
 #endif
 
 catchIO :: IO a -> (IOException -> IO a) -> IO a
-#if __GLASGOW_HASKELL__ >= 609
 catchIO = catch
-#else
-catchIO io handler = io `catch` handler'
-    where handler' (IOException ioe) = handler ioe
-          handler' e                 = throw e
-#endif
 
 handleIO :: (IOException -> IO a) -> IO a -> IO a
 handleIO = flip catchIO
 
 tryIO :: IO a -> IO (Either IOException a)
-#if __GLASGOW_HASKELL__ >= 609
 tryIO = try
-#else
-tryIO io = do ei <- try io
-              case ei of
-                  Right v -> return (Right v)
-                  Left (IOException ioe) -> return (Left ioe)
-                  Left e -> throwIO e
-#endif
 
 -- | A monad that can catch exceptions.  A minimal definition
 -- requires a definition of 'gcatch'.
 --
--- Although, 'gbracket' and 'gfinally' could be modelled on top of 'gcatch',
--- they are included in the type class since GHC needs special implementations
--- of these in order to properly handle asynchronous exceptions.
+-- Implementations on top of 'IO' should implement 'gblock' and 'gunblock' to
+-- eventually call the primitives 'Control.Exception.block' and
+-- 'Control.Exception.unblock' respectively.  These are used for
+-- implementations that support asynchronous exceptions.  The default
+-- implementations of 'gbracket' and 'gfinally' use 'gblock' and 'gunblock'
+-- thus rarely require overriding.
+--
 class Monad m => ExceptionMonad m where
+
   -- | Generalised version of 'Control.Exception.catch', allowing an arbitrary
   -- exception handling monad instead of just 'IO'.
-#if __GLASGOW_HASKELL__ >= 609
   gcatch :: Exception e => m a -> (e -> m a) -> m a
-#else
-  gcatch :: m a -> (Exception -> m a) -> m a
-  gcatchDyn :: Typeable e => m a -> (e -> m a) -> m a
-#endif
+
+  -- | Generalised version of 'Control.Exception.block', allowing an arbitrary
+  -- exception handling monad instead of just 'IO'.
+  gblock :: m a -> m a
+
+  -- | Generalised version of 'Control.Exception.unblock', allowing an
+  -- arbitrary exception handling monad instead of just 'IO'.
+  gunblock :: m a -> m a
 
   -- | Generalised version of 'Control.Exception.bracket', allowing an arbitrary
   -- exception handling monad instead of just 'IO'.
@@ -66,50 +55,40 @@ class Monad m => ExceptionMonad m where
   -- exception handling monad instead of just 'IO'.
   gfinally :: m a -> m b -> m a
 
-  gbracket acquire release in_between = do
-      a <- acquire
-      r <- in_between a `gonException` release a
-      release a
-      return r
+  gblock = id
+  gunblock = id
 
-  gfinally thing cleanup = do
-      r <- thing `gonException` cleanup
-      cleanup
-      return r
+  gbracket before after thing =
+    gblock (do
+      a <- before
+      r <- gunblock (thing a) `gonException` after a
+      _ <- after a
+      return r)
+
+  a `gfinally` sequel =
+    gblock (do
+      r <- gunblock a `gonException` sequel
+      _ <- sequel
+      return r)
 
 instance ExceptionMonad IO where
   gcatch    = catch
-#if __GLASGOW_HASKELL__ < 609
-  gcatchDyn = catchDyn
-#endif
-  gbracket  = bracket
-  gfinally  = finally
-
+  gblock    = block
+  gunblock  = unblock
 
-#if __GLASGOW_HASKELL__ >= 609
 gtry :: (ExceptionMonad m, Exception e) => m a -> m (Either e a)
-#else
-gtry :: (ExceptionMonad m) => m a -> m (Either Exception a)
-#endif
 gtry act = gcatch (act >>= \a -> return (Right a))
                   (\e -> return (Left e))
 
 -- | Generalised version of 'Control.Exception.handle', allowing an arbitrary
 -- exception handling monad instead of just 'IO'.
-#if __GLASGOW_HASKELL__ >= 609
 ghandle :: (ExceptionMonad m, Exception e) => (e -> m a) -> m a -> m a
-#else
-ghandle :: (ExceptionMonad m) => (Exception -> m a) -> m a -> m a
-#endif
 ghandle = flip gcatch
 
 -- | Always executes the first argument.  If this throws an exception the
 -- second argument is executed and the exception is raised again.
 gonException :: (ExceptionMonad m) => m a -> m b -> m a
 gonException ioA cleanup = ioA `gcatch` \e ->
-                             do cleanup
-#if __GLASGOW_HASKELL__ >= 609
+                             do _ <- cleanup
                                 throw (e :: SomeException)
-#else
-                                throw e
-#endif
+