AsyncException(..), -- instance Eq, Ord, Show, Typeable
-- * Throwing exceptions
+ throwIO, -- :: Exception -> IO a
throw, -- :: Exception -> a
- ioError, -- :: Exception -> IO a
+ ioError, -- :: IOError -> IO a
+#ifdef __GLASGOW_HASKELL__
throwTo, -- :: ThreadId -> Exception -> a
+#endif
-- * Catching Exceptions
-- ** The @evaluate@ function
evaluate, -- :: a -> IO a
+ -- ** The @mapException@ function
+ mapException, -- :: (Exception -> Exception) -> a -> a
+
-- ** Exception predicates
-- $preds
-- $dynamic
throwDyn, -- :: Typeable ex => ex -> b
+#ifdef __GLASGOW_HASKELL__
throwDynTo, -- :: Typeable ex => ThreadId -> ex -> b
+#endif
catchDyn, -- :: Typeable ex => IO a -> (ex -> IO a) -> IO a
-- * Asynchronous Exceptions
) where
#ifdef __GLASGOW_HASKELL__
-import Prelude hiding (catch)
-import System.IO.Error
import GHC.Base ( assert )
-import GHC.Exception hiding (try, catch, bracket, bracket_)
+import GHC.Exception as ExceptionBase hiding (catch)
import GHC.Conc ( throwTo, ThreadId )
import GHC.IOBase ( IO(..) )
#endif
#ifdef __HUGS__
-import Prelude hiding ( catch )
-import PrelPrim ( catchException
- , Exception(..)
- , throw
- , ArithException(..)
- , AsyncException(..)
- , assert
- )
+import Hugs.Exception as ExceptionBase
#endif
+import Prelude hiding ( catch )
+import System.IO.Error hiding ( catch, try )
+import System.IO.Unsafe (unsafePerformIO)
import Data.Dynamic
#include "Dynamic.h"
--
-- Note that 'catch' catches all types of exceptions, and is generally
-- used for \"cleaning up\" before passing on the exception using
--- 'ioError'. It is not good practice to discard the exception and
+-- 'throwIO'. It is not good practice to discard the exception and
-- continue, without first checking the type of the exception (it
-- might be a 'ThreadKilled', for example). In this case it is usually better
-- to use 'catchJust' and select the kinds of exceptions to catch.
catch :: IO a -- ^ The computation to run
-> (Exception -> IO a) -- ^ Handler to invoke if an exception is raised
-> IO a
-catch = GHC.Exception.catchException
+catch = ExceptionBase.catchException
-- | The function 'catchJust' is like 'catch', but it takes an extra
-- argument which is an /exception predicate/, a function which
-- > catch (evaluate undefined) (\e -> return ()) ==> return ()
--
-- NOTE: @(evaluate a)@ is /not/ the same as @(a \`seq\` return a)@.
+#ifdef __GLASGOW_HASKELL__
evaluate :: a -> IO a
-evaluate a = IO $ \s -> a `seq` (# s, a #)
+evaluate a = IO $ \s -> case a `seq` () of () -> (# s, a #)
+ -- NB. can't write
+ -- a `seq` (# s, a #)
+ -- because we can't have an unboxed tuple as a function argument
+#endif
+
+-----------------------------------------------------------------------------
+-- 'mapException'
+
+-- | This function maps one exception into another as proposed in the
+-- paper \"A semantics for imprecise exceptions\".
+
+-- Notice that the usage of 'unsafePerformIO' is safe here.
+
+mapException :: (Exception -> Exception) -> a -> a
+mapException f v = unsafePerformIO (catch (evaluate v)
+ (\x -> throw (f x)))
-----------------------------------------------------------------------------
-- 'try' and variations.
-- Dynamic exceptions
-- $dynamic
--- Because the 'Exception' datatype is not extensible, there is an
+-- #DynamicExceptions# Because the 'Exception' datatype is not extensible, there is an
-- interface for throwing and catching exceptions of type 'Dynamic'
-- (see "Data.Dynamic") which allows exception values of any type in
-- the 'Typeable' class to be thrown and caught.
throwDyn :: Typeable exception => exception -> b
throwDyn exception = throw (DynException (toDyn exception))
+#ifdef __GLASGOW_HASKELL__
-- | A variant of 'throwDyn' that throws the dynamic exception to an
--- arbitrary thread (c.f. 'throwTo').
+-- arbitrary thread (GHC only: c.f. 'throwTo').
throwDynTo :: Typeable exception => ThreadId -> exception -> IO ()
throwDynTo t exception = throwTo t (DynException (toDyn exception))
+#endif /* __GLASGOW_HASKELL__ */
-- | Catch dynamic exceptions of the required type. All other
-- exceptions are re-thrown, including dynamic exceptions of the wrong
ioErrors :: Exception -> Maybe IOError
arithExceptions :: Exception -> Maybe ArithException
errorCalls :: Exception -> Maybe String
-dynExceptions :: Exception -> Maybe Dynamic
assertions :: Exception -> Maybe String
+dynExceptions :: Exception -> Maybe Dynamic
asyncExceptions :: Exception -> Maybe AsyncException
userErrors :: Exception -> Maybe String
-ioErrors e@(IOException _) = Just e
+ioErrors (IOException e) = Just e
ioErrors _ = Nothing
arithExceptions (ArithException e) = Just e
asyncExceptions (AsyncException e) = Just e
asyncExceptions _ = Nothing
-userErrors e | isUserError e = Just (ioeGetErrorString e)
+userErrors (IOException e) | isUserError e = Just (ioeGetErrorString e)
userErrors _ = Nothing
-----------------------------------------------------------------------------
{- $async
-Asynchronous exceptions are so-called because they arise due to
+ #AsynchronousExceptions# Asynchronous exceptions are so-called because they arise due to
external influences, and can be raised at any point during execution.
'StackOverflow' and 'HeapOverflow' are two examples of
system-generated asynchronous exceptions.
-- returned as the result.
assert :: Bool -> a -> a
#endif
+
+#ifndef __GLASGOW_HASKELL__
+assert :: Bool -> a -> a
+assert True x = x
+assert False _ = throw (AssertionFailed "")
+#endif
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