X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Futils%2FException.hs;h=c51c2329ca870beced028c3520a0fe0abd57da0e;hb=aedb94f5f220b5e442b23ecc445fd38c8d9b6ba0;hp=11172b59b176e95fa28def02d02d7013d29378f8;hpb=aa9a4f1053d3c554629a2ec25955e7530c95b892;p=ghc-hetmet.git

diff --git a/compiler/utils/Exception.hs b/compiler/utils/Exception.hs
index 11172b5..c51c232 100644
--- a/compiler/utils/Exception.hs
+++ b/compiler/utils/Exception.hs
@@ -1,19 +1,94 @@
 
 module Exception
     (
-#if __GLASGOW_HASKELL__ >= 609
-    module Control.OldException
-#else
-    module Control.Exception
-#endif
+    module Control.Exception,
+    module Exception
     )
     where
 
-import Prelude ()
+import Prelude hiding (catch)
 
-#if __GLASGOW_HASKELL__ >= 609
-import Control.OldException
+#if __GLASGOW_HASKELL__ < 609
+import Control.Exception.Extensible as Control.Exception
 #else
 import Control.Exception
 #endif
 
+catchIO :: IO a -> (IOException -> IO a) -> IO a
+catchIO = catch
+
+handleIO :: (IOException -> IO a) -> IO a -> IO a
+handleIO = flip catchIO
+
+tryIO :: IO a -> IO (Either IOException a)
+tryIO = try
+
+-- | A monad that can catch exceptions.  A minimal definition
+-- requires a definition of 'gcatch'.
+--
+-- 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'.
+  gcatch :: Exception e => m a -> (e -> m a) -> m a
+
+  -- | 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'.
+  gbracket :: m a -> (a -> m b) -> (a -> m c) -> m c
+
+  -- | Generalised version of 'Control.Exception.finally', allowing an arbitrary
+  -- exception handling monad instead of just 'IO'.
+  gfinally :: m a -> m b -> m a
+
+  gblock = id
+  gunblock = id
+
+  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
+  gblock    = block
+  gunblock  = unblock
+
+gtry :: (ExceptionMonad m, Exception e) => m a -> m (Either e a)
+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'.
+ghandle :: (ExceptionMonad m, Exception e) => (e -> m a) -> m a -> m a
+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
+                                throw (e :: SomeException)
+