+{-# OPTIONS_GHC -XNoImplicitPrelude #-}
+
+#include "Typeable.h"
+
-----------------------------------------------------------------------------
-- |
-- Module : Control.Exception
module Control.Exception (
- -- * The Exception type
- Exception(..), -- instance Eq, Ord, Show, Typeable
- IOException, -- instance Eq, Ord, Show, Typeable
- ArithException(..), -- instance Eq, Ord, Show, Typeable
- ArrayException(..), -- instance Eq, Ord, Show, Typeable
- AsyncException(..), -- instance Eq, Ord, Show, Typeable
-
- -- * Throwing exceptions
- throwIO, -- :: Exception -> IO a
- throw, -- :: Exception -> a
- ioError, -- :: IOError -> IO a
+ -- * The Exception type
+ SomeException(..),
+ Exception(..), -- instance Eq, Ord, Show, Typeable
+ IOException, -- instance Eq, Ord, Show, Typeable
+ ArithException(..), -- instance Eq, Ord, Show, Typeable
+ ArrayException(..), -- instance Eq, Ord, Show, Typeable
+ AssertionFailed(..),
+ AsyncException(..), -- instance Eq, Ord, Show, Typeable
+ NonTermination(..), nonTermination,
+ BlockedOnDeadMVar(..),
+ BlockedIndefinitely(..),
+ NestedAtomically(..), nestedAtomically,
+ Deadlock(..),
+ NoMethodError(..),
+ PatternMatchFail(..),
+ RecConError(..),
+ RecSelError(..),
+ RecUpdError(..),
+ ErrorCall(..),
+
+ -- * Throwing exceptions
+ throwIO, -- :: Exception -> IO a
+ throw, -- :: Exception -> a
+ ioError, -- :: IOError -> IO a
#ifdef __GLASGOW_HASKELL__
- throwTo, -- :: ThreadId -> Exception -> a
+ throwTo, -- :: ThreadId -> Exception -> a
#endif
- -- * Catching Exceptions
-
- -- |There are several functions for catching and examining
- -- exceptions; all of them may only be used from within the
- -- 'IO' monad.
-
- -- ** The @catch@ functions
- catch, -- :: IO a -> (Exception -> IO a) -> IO a
- catchJust, -- :: (Exception -> Maybe b) -> IO a -> (b -> IO a) -> IO a
-
- -- ** The @handle@ functions
- handle, -- :: (Exception -> IO a) -> IO a -> IO a
- handleJust,-- :: (Exception -> Maybe b) -> (b -> IO a) -> IO a -> IO a
+ -- * Catching Exceptions
- -- ** The @try@ functions
- try, -- :: IO a -> IO (Either Exception a)
- tryJust, -- :: (Exception -> Maybe b) -> a -> IO (Either b a)
+ -- |There are several functions for catching and examining
+ -- exceptions; all of them may only be used from within the
+ -- 'IO' monad.
- -- ** The @evaluate@ function
- evaluate, -- :: a -> IO a
+ -- ** The @catch@ functions
+ catch, -- :: IO a -> (Exception -> IO a) -> IO a
+ catches, Handler(..),
+ catchJust, -- :: (Exception -> Maybe b) -> IO a -> (b -> IO a) -> IO a
- -- ** The @mapException@ function
- mapException, -- :: (Exception -> Exception) -> a -> a
+ -- ** The @handle@ functions
+ handle, -- :: (Exception -> IO a) -> IO a -> IO a
+ handleJust,-- :: (Exception -> Maybe b) -> (b -> IO a) -> IO a -> IO a
- -- ** Exception predicates
-
- -- $preds
+ -- ** The @try@ functions
+ try, -- :: IO a -> IO (Either Exception a)
+ tryJust, -- :: (Exception -> Maybe b) -> a -> IO (Either b a)
+ onException,
- ioErrors, -- :: Exception -> Maybe IOError
- arithExceptions, -- :: Exception -> Maybe ArithException
- errorCalls, -- :: Exception -> Maybe String
- dynExceptions, -- :: Exception -> Maybe Dynamic
- assertions, -- :: Exception -> Maybe String
- asyncExceptions, -- :: Exception -> Maybe AsyncException
- userErrors, -- :: Exception -> Maybe String
+ -- ** The @evaluate@ function
+ evaluate, -- :: a -> IO a
- -- * Dynamic exceptions
+ -- ** The @mapException@ function
+ mapException, -- :: (Exception -> Exception) -> a -> a
- -- $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
+ -- * Asynchronous Exceptions
- -- $async
+ -- $async
- -- ** Asynchronous exception control
+ -- ** Asynchronous exception control
- -- |The following two functions allow a thread to control delivery of
- -- asynchronous exceptions during a critical region.
+ -- |The following two functions allow a thread to control delivery of
+ -- asynchronous exceptions during a critical region.
block, -- :: IO a -> IO a
unblock, -- :: IO a -> IO a
+ blocked, -- :: IO Bool
- -- *** Applying @block@ to an exception handler
+ -- *** Applying @block@ to an exception handler
- -- $block_handler
+ -- $block_handler
- -- *** Interruptible operations
+ -- *** Interruptible operations
- -- $interruptible
+ -- $interruptible
- -- * Assertions
+ -- * Assertions
- assert, -- :: Bool -> a -> a
+ assert, -- :: Bool -> a -> a
- -- * Utilities
+ -- * Utilities
- bracket, -- :: IO a -> (a -> IO b) -> (a -> IO c) -> IO ()
- bracket_, -- :: IO a -> IO b -> IO c -> IO ()
- bracketOnError,
+ bracket, -- :: IO a -> (a -> IO b) -> (a -> IO c) -> IO ()
+ bracket_, -- :: IO a -> IO b -> IO c -> IO ()
+ bracketOnError,
- finally, -- :: IO a -> IO b -> IO a
-
-#ifdef __GLASGOW_HASKELL__
- setUncaughtExceptionHandler, -- :: (Exception -> IO ()) -> IO ()
- getUncaughtExceptionHandler -- :: IO (Exception -> IO ())
-#endif
+ finally, -- :: IO a -> IO b -> IO a
+
+ recSelError, recConError, irrefutPatError, runtimeError,
+ nonExhaustiveGuardsError, patError, noMethodBindingError,
+ assertError,
) where
#ifdef __GLASGOW_HASKELL__
-import GHC.Base ( assert )
-import GHC.Exception as ExceptionBase hiding (catch)
-import GHC.Conc ( throwTo, ThreadId )
-import Data.IORef ( IORef, newIORef, readIORef, writeIORef )
-import Foreign.C.String ( CString, withCString )
-import System.IO ( stdout, hFlush )
+import GHC.Base
+import GHC.IOBase
+import GHC.List
+import GHC.Show
+import GHC.IOBase as ExceptionBase
+import GHC.Exception hiding ( Exception )
+import GHC.Conc
#endif
#ifdef __HUGS__
-import Hugs.Exception as ExceptionBase
+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
+import Data.Either
+import Data.Maybe
#ifdef __NHC__
-import System.IO.Error (catch, ioError)
+import qualified System.IO.Error as H'98 (catch)
+import System.IO.Error (ioError)
import IO (bracket)
-import DIOError -- defn of IOError type
+import DIOError -- defn of IOError type
+import System (ExitCode())
-- minimum needed for nhc98 to pretend it has Exceptions
-type Exception = IOError
+data Exception = IOException IOException
+ | ArithException ArithException
+ | ArrayException ArrayException
+ | AsyncException AsyncException
+ | ExitException ExitCode
+ deriving Show
type IOException = IOError
data ArithException
data ArrayException
data AsyncException
-
-throwIO :: Exception -> IO a
-throwIO = ioError
-throw :: Exception -> a
+instance Show ArithException
+instance Show ArrayException
+instance Show AsyncException
+
+catch :: IO a -> (Exception -> IO a) -> IO a
+a `catch` b = a `H'98.catch` (b . IOException)
+
+throwIO :: Exception -> IO a
+throwIO (IOException e) = ioError e
+throwIO _ = ioError (UserError "Control.Exception.throwIO"
+ "unknown exception")
+throw :: Exception -> a
throw = unsafePerformIO . throwIO
evaluate :: a -> IO a
evaluate x = x `seq` return x
-ioErrors :: Exception -> Maybe IOError
-ioErrors e = Just e
-arithExceptions :: Exception -> Maybe ArithException
-arithExceptions = const Nothing
-errorCalls :: Exception -> Maybe String
-errorCalls = const Nothing
-dynExceptions :: Exception -> Maybe Dynamic
-dynExceptions = const Nothing
-assertions :: Exception -> Maybe String
-assertions = const Nothing
-asyncExceptions :: Exception -> Maybe AsyncException
-asyncExceptions = const Nothing
-userErrors :: Exception -> Maybe String
-userErrors (UserError _ s) = Just s
-userErrors _ = Nothing
+assert :: Bool -> a -> a
+assert True x = x
+assert False _ = throw (IOException (UserError "" "Assertion failed"))
+#endif
+
+#ifndef __GLASGOW_HASKELL__
+-- Dummy definitions for implementations lacking asynchonous exceptions
block :: IO a -> IO a
block = id
unblock :: IO a -> IO a
unblock = id
-
-assert :: Bool -> a -> a
-assert True x = x
-assert False _ = throw (UserError "" "Assertion failed")
+blocked :: IO Bool
+blocked = return False
#endif
-----------------------------------------------------------------------------
-- and then using @C.catch@
--
#ifndef __NHC__
-catch :: IO a -- ^ The computation to run
- -> (Exception -> IO a) -- ^ Handler to invoke if an exception is raised
- -> IO a
-catch = ExceptionBase.catchException
+catch :: Exception e
+ => IO a -- ^ The computation to run
+ -> (e -> IO a) -- ^ Handler to invoke if an exception is raised
+ -> IO a
+catch = ExceptionBase.catchException
+
+catches :: IO a -> [Handler a] -> IO a
+catches io handlers = io `catch` catchesHandler handlers
+
+catchesHandler :: [Handler a] -> SomeException -> IO a
+catchesHandler handlers e = foldr tryHandler (throw e) handlers
+ where tryHandler (Handler handler) res
+ = case fromException e of
+ Just e' -> handler e'
+ Nothing -> res
+
+data Handler a = forall e . Exception e => Handler (e -> IO a)
#endif
-- | The function 'catchJust' is like 'catch', but it takes an extra
-- argument which is an /exception predicate/, a function which
--- selects which type of exceptions we\'re interested in. There are
--- some predefined exception predicates for useful subsets of
--- exceptions: 'ioErrors', 'arithExceptions', and so on. For example,
--- to catch just calls to the 'error' function, we could use
+-- selects which type of exceptions we\'re interested in.
--
-- > result <- catchJust errorCalls thing_to_try handler
--
-- are re-raised, and may be caught by an enclosing
-- 'catch' or 'catchJust'.
catchJust
- :: (Exception -> Maybe b) -- ^ Predicate to select exceptions
- -> IO a -- ^ Computation to run
- -> (b -> IO a) -- ^ Handler
- -> IO a
+ :: Exception e
+ => (e -> Maybe b) -- ^ Predicate to select exceptions
+ -> IO a -- ^ Computation to run
+ -> (b -> IO a) -- ^ Handler
+ -> IO a
catchJust p a handler = catch a handler'
where handler' e = case p e of
- Nothing -> throw e
- Just b -> handler b
+ Nothing -> throw e
+ Just b -> handler b
-- | A version of 'catch' with the arguments swapped around; useful in
-- situations where the code for the handler is shorter. For example:
--
-- > do handle (\e -> exitWith (ExitFailure 1)) $
--- > ...
-handle :: (Exception -> IO a) -> IO a -> IO a
+-- > ...
+handle :: Exception e => (e -> IO a) -> IO a -> IO a
handle = flip catch
-- | A version of 'catchJust' with the arguments swapped around (see
-- 'handle').
-handleJust :: (Exception -> Maybe b) -> (b -> IO a) -> IO a -> IO a
+handleJust :: Exception e => (e -> Maybe b) -> (b -> IO a) -> IO a -> IO a
handleJust p = flip (catchJust p)
-----------------------------------------------------------------------------
-- Notice that the usage of 'unsafePerformIO' is safe here.
-mapException :: (Exception -> Exception) -> a -> a
+mapException :: Exception e => (e -> e) -> a -> a
mapException f v = unsafePerformIO (catch (evaluate v)
(\x -> throw (f x)))
-- except that it catches only the IO and user families of exceptions
-- (as required by the Haskell 98 @IO@ module).
-try :: IO a -> IO (Either Exception a)
+try :: Exception e => IO a -> IO (Either e a)
try a = catch (a >>= \ v -> return (Right v)) (\e -> return (Left e))
-- | A variant of 'try' that takes an exception predicate to select
-- which exceptions are caught (c.f. 'catchJust'). If the exception
-- does not match the predicate, it is re-thrown.
-tryJust :: (Exception -> Maybe b) -> IO a -> IO (Either b a)
+tryJust :: Exception e => (e -> Maybe b) -> IO a -> IO (Either b a)
tryJust p a = do
r <- try a
case r of
- Right v -> return (Right v)
- Left e -> case p e of
- Nothing -> throw e
- Just b -> return (Left b)
-
------------------------------------------------------------------------------
--- Dynamic exceptions
-
--- $dynamic
--- #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.
-
--- | Raise any value as an exception, provided it is in the
--- 'Typeable' class.
-throwDyn :: Typeable exception => exception -> b
-#ifdef __NHC__
-throwDyn exception = throw (UserError "" "dynamic exception")
-#else
-throwDyn exception = throw (DynException (toDyn exception))
-#endif
-
-#ifdef __GLASGOW_HASKELL__
--- | A variant of 'throwDyn' that throws the dynamic exception to an
--- 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
--- type.
---
--- When using dynamic exceptions it is advisable to define a new
--- datatype to use for your exception type, to avoid possible clashes
--- with dynamic exceptions used in other libraries.
---
-catchDyn :: Typeable exception => IO a -> (exception -> IO a) -> IO a
-#ifdef __NHC__
-catchDyn m k = m -- can't catch dyn exceptions in nhc98
-#else
-catchDyn m k = catchException m handle
- where handle ex = case ex of
- (DynException dyn) ->
- case fromDynamic dyn of
- Just exception -> k exception
- Nothing -> throw ex
- _ -> throw ex
-#endif
-
------------------------------------------------------------------------------
--- Exception Predicates
-
--- $preds
--- These pre-defined predicates may be used as the first argument to
--- 'catchJust', 'tryJust', or 'handleJust' to select certain common
--- classes of exceptions.
-#ifndef __NHC__
-ioErrors :: Exception -> Maybe IOError
-arithExceptions :: Exception -> Maybe ArithException
-errorCalls :: Exception -> Maybe String
-assertions :: Exception -> Maybe String
-dynExceptions :: Exception -> Maybe Dynamic
-asyncExceptions :: Exception -> Maybe AsyncException
-userErrors :: Exception -> Maybe String
-
-ioErrors (IOException e) = Just e
-ioErrors _ = Nothing
-
-arithExceptions (ArithException e) = Just e
-arithExceptions _ = Nothing
-
-errorCalls (ErrorCall e) = Just e
-errorCalls _ = Nothing
-
-assertions (AssertionFailed e) = Just e
-assertions _ = Nothing
+ Right v -> return (Right v)
+ Left e -> case p e of
+ Nothing -> throw e
+ Just b -> return (Left b)
-dynExceptions (DynException e) = Just e
-dynExceptions _ = Nothing
+onException :: IO a -> IO b -> IO a
+onException io what = io `catch` \e -> do what
+ throw (e :: SomeException)
-asyncExceptions (AsyncException e) = Just e
-asyncExceptions _ = Nothing
-
-userErrors (IOException e) | isUserError e = Just (ioeGetErrorString e)
-userErrors _ = Nothing
-#endif
-----------------------------------------------------------------------------
-- Some Useful Functions
--
#ifndef __NHC__
bracket
- :: IO a -- ^ computation to run first (\"acquire resource\")
- -> (a -> IO b) -- ^ computation to run last (\"release resource\")
- -> (a -> IO c) -- ^ computation to run in-between
- -> IO c -- returns the value from the in-between computation
+ :: IO a -- ^ computation to run first (\"acquire resource\")
+ -> (a -> IO b) -- ^ computation to run last (\"release resource\")
+ -> (a -> IO c) -- ^ computation to run in-between
+ -> IO c -- returns the value from the in-between computation
bracket before after thing =
block (do
a <- before
- r <- catch
- (unblock (thing a))
- (\e -> do { after a; throw e })
+ r <- unblock (thing a) `onException` after a
after a
return r
)
-- | A specialised variant of 'bracket' with just a computation to run
-- afterward.
--
-finally :: IO a -- ^ computation to run first
- -> IO b -- ^ computation to run afterward (even if an exception
- -- was raised)
- -> IO a -- returns the value from the first computation
+finally :: IO a -- ^ computation to run first
+ -> IO b -- ^ computation to run afterward (even if an exception
+ -- was raised)
+ -> IO a -- returns the value from the first computation
a `finally` sequel =
block (do
- r <- catch
- (unblock a)
- (\e -> do { sequel; throw e })
+ r <- unblock a `onException` sequel
sequel
return r
)
-- | Like bracket, but only performs the final action if there was an
-- exception raised by the in-between computation.
bracketOnError
- :: IO a -- ^ computation to run first (\"acquire resource\")
- -> (a -> IO b) -- ^ computation to run last (\"release resource\")
- -> (a -> IO c) -- ^ computation to run in-between
- -> IO c -- returns the value from the in-between computation
+ :: IO a -- ^ computation to run first (\"acquire resource\")
+ -> (a -> IO b) -- ^ computation to run last (\"release resource\")
+ -> (a -> IO c) -- ^ computation to run in-between
+ -> IO c -- returns the value from the in-between computation
bracketOnError before after thing =
block (do
a <- before
- catch
- (unblock (thing a))
- (\e -> do { after a; throw e })
+ unblock (thing a) `onException` after a
)
-- -----------------------------------------------------------------------------
assert False _ = throw (AssertionFailed "")
#endif
+recSelError, recConError, irrefutPatError, runtimeError,
+ nonExhaustiveGuardsError, patError, noMethodBindingError
+ :: Addr# -> a -- All take a UTF8-encoded C string
+
+recSelError s = throw (RecSelError (unpackCStringUtf8# s)) -- No location info unfortunately
+runtimeError s = error (unpackCStringUtf8# s) -- No location info unfortunately
+
+nonExhaustiveGuardsError s = throw (PatternMatchFail (untangle s "Non-exhaustive guards in"))
+irrefutPatError s = throw (PatternMatchFail (untangle s "Irrefutable pattern failed for pattern"))
+recConError s = throw (RecConError (untangle s "Missing field in record construction"))
+noMethodBindingError s = throw (NoMethodError (untangle s "No instance nor default method for class operation"))
+patError s = throw (PatternMatchFail (untangle s "Non-exhaustive patterns in"))
+
+-----
+
+data PatternMatchFail = PatternMatchFail String
+INSTANCE_TYPEABLE0(PatternMatchFail,patternMatchFailTc,"PatternMatchFail")
+
+instance Exception PatternMatchFail
+
+instance Show PatternMatchFail where
+ showsPrec _ (PatternMatchFail err) = showString err
+
+-----
+
+data RecSelError = RecSelError String
+INSTANCE_TYPEABLE0(RecSelError,recSelErrorTc,"RecSelError")
+
+instance Exception RecSelError
+
+instance Show RecSelError where
+ showsPrec _ (RecSelError err) = showString err
+
+-----
+
+data RecConError = RecConError String
+INSTANCE_TYPEABLE0(RecConError,recConErrorTc,"RecConError")
+
+instance Exception RecConError
+
+instance Show RecConError where
+ showsPrec _ (RecConError err) = showString err
+
+-----
+
+data RecUpdError = RecUpdError String
+INSTANCE_TYPEABLE0(RecUpdError,recUpdErrorTc,"RecUpdError")
+
+instance Exception RecUpdError
+
+instance Show RecUpdError where
+ showsPrec _ (RecUpdError err) = showString err
+
+-----
+
+data NoMethodError = NoMethodError String
+INSTANCE_TYPEABLE0(NoMethodError,noMethodErrorTc,"NoMethodError")
+
+instance Exception NoMethodError
+
+instance Show NoMethodError where
+ showsPrec _ (NoMethodError err) = showString err
+
+-----
+
+data NonTermination = NonTermination
+INSTANCE_TYPEABLE0(NonTermination,nonTerminationTc,"NonTermination")
+
+instance Exception NonTermination
+
+instance Show NonTermination where
+ showsPrec _ NonTermination = showString "<<loop>>"
+
+-- GHC's RTS calls this
+nonTermination :: SomeException
+nonTermination = toException NonTermination
+
+-----
+
+data NestedAtomically = NestedAtomically
+INSTANCE_TYPEABLE0(NestedAtomically,nestedAtomicallyTc,"NestedAtomically")
+
+instance Exception NestedAtomically
+
+instance Show NestedAtomically where
+ showsPrec _ NestedAtomically = showString "Control.Concurrent.STM.atomically was nested"
+
+-- GHC's RTS calls this
+nestedAtomically :: SomeException
+nestedAtomically = toException NestedAtomically
+
+-----
+
+instance Exception Dynamic
-#ifdef __GLASGOW_HASKELL__
-{-# NOINLINE uncaughtExceptionHandler #-}
-uncaughtExceptionHandler :: IORef (Exception -> IO ())
-uncaughtExceptionHandler = unsafePerformIO (newIORef defaultHandler)
- where
- defaultHandler :: Exception -> IO ()
- defaultHandler ex = do
- (hFlush stdout) `catchException` (\ _ -> return ())
- let msg = case ex of
- Deadlock -> "no threads to run: infinite loop or deadlock?"
- ErrorCall s -> s
- other -> showsPrec 0 other ""
- withCString "%s" $ \cfmt ->
- withCString msg $ \cmsg ->
- errorBelch cfmt cmsg
-
-foreign import ccall unsafe "RtsMessages.h errorBelch"
- errorBelch :: CString -> CString -> IO ()
-
-setUncaughtExceptionHandler :: (Exception -> IO ()) -> IO ()
-setUncaughtExceptionHandler = writeIORef uncaughtExceptionHandler
-
-getUncaughtExceptionHandler :: IO (Exception -> IO ())
-getUncaughtExceptionHandler = readIORef uncaughtExceptionHandler
-#endif
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