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Diffstat (limited to 'compiler/GHC/Utils/Exception.hs')
-rw-r--r-- | compiler/GHC/Utils/Exception.hs | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/compiler/GHC/Utils/Exception.hs b/compiler/GHC/Utils/Exception.hs new file mode 100644 index 0000000000..e84221cdbe --- /dev/null +++ b/compiler/GHC/Utils/Exception.hs @@ -0,0 +1,83 @@ +{-# OPTIONS_GHC -fno-warn-deprecations #-} +module GHC.Utils.Exception + ( + module Control.Exception, + module GHC.Utils.Exception + ) + where + +import GHC.Prelude + +import Control.Exception +import Control.Monad.IO.Class + +catchIO :: IO a -> (IOException -> IO a) -> IO a +catchIO = Control.Exception.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 'gmask' to +-- eventually call the primitive 'Control.Exception.mask'. +-- These are used for +-- implementations that support asynchronous exceptions. The default +-- implementations of 'gbracket' and 'gfinally' use 'gmask' +-- thus rarely require overriding. +-- +class MonadIO 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 + + 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 + +instance ExceptionMonad IO where + gcatch = Control.Exception.catch + gmask f = mask (\x -> f x) + +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 + liftIO $ throwIO (e :: SomeException) + |