update submodule pointer

[ghc-hetmet.git] / compiler / utils / Exception.hs

diff --git a/compiler/utils/Exception.hs b/compiler/utils/Exception.hs
index 11172b5..fa067b0 100644 (file)
--- a/compiler/utils/Exception.hs
+++ b/compiler/utils/Exception.hs
@@ -1,19 +1,106 @@
-
+{-# OPTIONS_GHC -fno-warn-deprecations #-}
 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
-#else
 import Control.Exception
+
+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.mask_', allowing an arbitrary
+  -- exception handling monad instead of just 'IO'.
+  gmask :: ((m a -> m a) -> m b) -> m b
+
+  -- | 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
+
+  -- | DEPRECATED, here for backwards compatibilty.  Instances can
+  -- define either 'gmask', or both 'block' and 'unblock'.
+  gblock   :: m a -> m a
+  -- | DEPRECATED, here for backwards compatibilty  Instances can
+  -- define either 'gmask', or both 'block' and 'unblock'.
+  gunblock :: m a -> m a
+  -- XXX we're keeping these two methods for the time being because we
+  -- have to interact with Haskeline's MonadException class which
+  -- still has block/unblock; see GhciMonad.hs.
+
+  gmask    f = gblock (f gunblock)
+  gblock   f = gmask (\_ -> f)
+  gunblock f = f -- XXX wrong; better override this if you need it
+
+  gbracket before after thing =
+    gmask $ \restore -> do
+      a <- before
+      r <- restore (thing a) `gonException` after a
+      _ <- after a
+      return r
+
+  a `gfinally` sequel =
+    gmask $ \restore -> do
+      r <- restore a `gonException` sequel
+      _ <- sequel
+      return r
+
+#if __GLASGOW_HASKELL__ < 613
+instance ExceptionMonad IO where
+  gcatch    = catch
+  gmask f   = block $ f unblock
+  gblock    = block
+  gunblock  = unblock
+#else
+instance ExceptionMonad IO where
+  gcatch    = catch
+  gmask f   = mask (\x -> f x)
+  gblock    = block
+  gunblock  = unblock
 #endif
 
+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)
+