1 {-# OPTIONS_GHC -XNoImplicitPrelude #-}
5 -----------------------------------------------------------------------------
7 -- Module : Control.OldException
8 -- Copyright : (c) The University of Glasgow 2001
9 -- License : BSD-style (see the file libraries/base/LICENSE)
11 -- Maintainer : libraries@haskell.org
12 -- Stability : experimental
13 -- Portability : non-portable (extended exceptions)
15 -- This module provides support for raising and catching both built-in
16 -- and user-defined exceptions.
18 -- In addition to exceptions thrown by 'IO' operations, exceptions may
19 -- be thrown by pure code (imprecise exceptions) or by external events
20 -- (asynchronous exceptions), but may only be caught in the 'IO' monad.
21 -- For more details, see:
23 -- * /A semantics for imprecise exceptions/, by Simon Peyton Jones,
24 -- Alastair Reid, Tony Hoare, Simon Marlow, Fergus Henderson,
27 -- * /Asynchronous exceptions in Haskell/, by Simon Marlow, Simon Peyton
28 -- Jones, Andy Moran and John Reppy, in /PLDI'01/.
30 -----------------------------------------------------------------------------
32 module Control.OldException {-# DEPRECATED "Future versions of base will not support the old exceptions style. Please switch to extensible exceptions." #-} (
34 -- * The Exception type
35 Exception(..), -- instance Eq, Ord, Show, Typeable
36 New.IOException, -- instance Eq, Ord, Show, Typeable
37 New.ArithException(..), -- instance Eq, Ord, Show, Typeable
38 New.ArrayException(..), -- instance Eq, Ord, Show, Typeable
39 New.AsyncException(..), -- instance Eq, Ord, Show, Typeable
41 -- * Throwing exceptions
42 throwIO, -- :: Exception -> IO a
43 throw, -- :: Exception -> a
44 ioError, -- :: IOError -> IO a
45 #ifdef __GLASGOW_HASKELL__
46 -- XXX Need to restrict the type of this:
47 New.throwTo, -- :: ThreadId -> Exception -> a
50 -- * Catching Exceptions
52 -- |There are several functions for catching and examining
53 -- exceptions; all of them may only be used from within the
56 -- ** The @catch@ functions
57 catch, -- :: IO a -> (Exception -> IO a) -> IO a
58 catchJust, -- :: (Exception -> Maybe b) -> IO a -> (b -> IO a) -> IO a
60 -- ** The @handle@ functions
61 handle, -- :: (Exception -> IO a) -> IO a -> IO a
62 handleJust,-- :: (Exception -> Maybe b) -> (b -> IO a) -> IO a -> IO a
64 -- ** The @try@ functions
65 try, -- :: IO a -> IO (Either Exception a)
66 tryJust, -- :: (Exception -> Maybe b) -> a -> IO (Either b a)
68 -- ** The @evaluate@ function
69 evaluate, -- :: a -> IO a
71 -- ** The @mapException@ function
72 mapException, -- :: (Exception -> Exception) -> a -> a
74 -- ** Exception predicates
78 ioErrors, -- :: Exception -> Maybe IOError
79 arithExceptions, -- :: Exception -> Maybe ArithException
80 errorCalls, -- :: Exception -> Maybe String
81 dynExceptions, -- :: Exception -> Maybe Dynamic
82 assertions, -- :: Exception -> Maybe String
83 asyncExceptions, -- :: Exception -> Maybe AsyncException
84 userErrors, -- :: Exception -> Maybe String
86 -- * Dynamic exceptions
89 throwDyn, -- :: Typeable ex => ex -> b
90 #ifdef __GLASGOW_HASKELL__
91 throwDynTo, -- :: Typeable ex => ThreadId -> ex -> b
93 catchDyn, -- :: Typeable ex => IO a -> (ex -> IO a) -> IO a
95 -- * Asynchronous Exceptions
99 -- ** Asynchronous exception control
101 -- |The following two functions allow a thread to control delivery of
102 -- asynchronous exceptions during a critical region.
104 block, -- :: IO a -> IO a
105 unblock, -- :: IO a -> IO a
107 -- *** Applying @block@ to an exception handler
111 -- *** Interruptible operations
117 assert, -- :: Bool -> a -> a
121 bracket, -- :: IO a -> (a -> IO b) -> (a -> IO c) -> IO ()
122 bracket_, -- :: IO a -> IO b -> IO c -> IO ()
125 finally, -- :: IO a -> IO b -> IO a
127 #ifdef __GLASGOW_HASKELL__
128 setUncaughtExceptionHandler, -- :: (Exception -> IO ()) -> IO ()
129 getUncaughtExceptionHandler -- :: IO (Exception -> IO ())
133 #ifdef __GLASGOW_HASKELL__
137 -- import GHC.IO ( IO )
138 import GHC.IO.Handle.FD ( stdout )
139 import qualified GHC.IO as New
140 import qualified GHC.IO.Exception as New
141 import GHC.Conc hiding (setUncaughtExceptionHandler,
142 getUncaughtExceptionHandler)
143 import Data.IORef ( IORef, newIORef, readIORef, writeIORef )
144 import Foreign.C.String ( CString, withCString )
145 import GHC.IO.Handle ( hFlush )
149 import Prelude hiding (catch)
150 import Hugs.Prelude as New (ExitCode(..))
153 import qualified Control.Exception as New
154 import Control.Exception ( toException, fromException, throw, block, unblock, mask, evaluate, throwIO )
155 import System.IO.Error hiding ( catch, try )
156 import System.IO.Unsafe (unsafePerformIO)
162 import System.IO.Error (catch, ioError)
164 import DIOError -- defn of IOError type
166 -- minimum needed for nhc98 to pretend it has Exceptions
167 type Exception = IOError
168 type IOException = IOError
173 throwIO :: Exception -> IO a
175 throw :: Exception -> a
176 throw = unsafePerformIO . throwIO
178 evaluate :: a -> IO a
179 evaluate x = x `seq` return x
181 ioErrors :: Exception -> Maybe IOError
183 arithExceptions :: Exception -> Maybe ArithException
184 arithExceptions = const Nothing
185 errorCalls :: Exception -> Maybe String
186 errorCalls = const Nothing
187 dynExceptions :: Exception -> Maybe Dynamic
188 dynExceptions = const Nothing
189 assertions :: Exception -> Maybe String
190 assertions = const Nothing
191 asyncExceptions :: Exception -> Maybe AsyncException
192 asyncExceptions = const Nothing
193 userErrors :: Exception -> Maybe String
194 userErrors (UserError _ s) = Just s
195 userErrors _ = Nothing
197 block :: IO a -> IO a
199 unblock :: IO a -> IO a
202 assert :: Bool -> a -> a
204 assert False _ = throw (UserError "" "Assertion failed")
207 -----------------------------------------------------------------------------
208 -- Catching exceptions
210 -- |This is the simplest of the exception-catching functions. It
211 -- takes a single argument, runs it, and if an exception is raised
212 -- the \"handler\" is executed, with the value of the exception passed as an
213 -- argument. Otherwise, the result is returned as normal. For example:
215 -- > catch (openFile f ReadMode)
216 -- > (\e -> hPutStr stderr ("Couldn't open "++f++": " ++ show e))
218 -- For catching exceptions in pure (non-'IO') expressions, see the
219 -- function 'evaluate'.
221 -- Note that due to Haskell\'s unspecified evaluation order, an
222 -- expression may return one of several possible exceptions: consider
223 -- the expression @error \"urk\" + 1 \`div\` 0@. Does
224 -- 'catch' execute the handler passing
225 -- @ErrorCall \"urk\"@, or @ArithError DivideByZero@?
227 -- The answer is \"either\": 'catch' makes a
228 -- non-deterministic choice about which exception to catch. If you
229 -- call it again, you might get a different exception back. This is
230 -- ok, because 'catch' is an 'IO' computation.
232 -- Note that 'catch' catches all types of exceptions, and is generally
233 -- used for \"cleaning up\" before passing on the exception using
234 -- 'throwIO'. It is not good practice to discard the exception and
235 -- continue, without first checking the type of the exception (it
236 -- might be a 'ThreadKilled', for example). In this case it is usually better
237 -- to use 'catchJust' and select the kinds of exceptions to catch.
239 -- Also note that the "Prelude" also exports a function called
240 -- 'Prelude.catch' with a similar type to 'Control.OldException.catch',
241 -- except that the "Prelude" version only catches the IO and user
242 -- families of exceptions (as required by Haskell 98).
244 -- We recommend either hiding the "Prelude" version of 'Prelude.catch'
245 -- when importing "Control.OldException":
247 -- > import Prelude hiding (catch)
249 -- or importing "Control.OldException" qualified, to avoid name-clashes:
251 -- > import qualified Control.OldException as C
253 -- and then using @C.catch@
256 catch :: IO a -- ^ The computation to run
257 -> (Exception -> IO a) -- ^ Handler to invoke if an exception is raised
259 -- note: bundling the exceptions is done in the New.Exception
260 -- instance of Exception; see below.
263 -- | The function 'catchJust' is like 'catch', but it takes an extra
264 -- argument which is an /exception predicate/, a function which
265 -- selects which type of exceptions we\'re interested in. There are
266 -- some predefined exception predicates for useful subsets of
267 -- exceptions: 'ioErrors', 'arithExceptions', and so on. For example,
268 -- to catch just calls to the 'error' function, we could use
270 -- > result <- catchJust errorCalls thing_to_try handler
272 -- Any other exceptions which are not matched by the predicate
273 -- are re-raised, and may be caught by an enclosing
274 -- 'catch' or 'catchJust'.
276 :: (Exception -> Maybe b) -- ^ Predicate to select exceptions
277 -> IO a -- ^ Computation to run
278 -> (b -> IO a) -- ^ Handler
280 catchJust p a handler = catch a handler'
281 where handler' e = case p e of
285 -- | A version of 'catch' with the arguments swapped around; useful in
286 -- situations where the code for the handler is shorter. For example:
288 -- > do handle (\e -> exitWith (ExitFailure 1)) $
290 handle :: (Exception -> IO a) -> IO a -> IO a
293 -- | A version of 'catchJust' with the arguments swapped around (see
295 handleJust :: (Exception -> Maybe b) -> (b -> IO a) -> IO a -> IO a
296 handleJust p = flip (catchJust p)
298 -----------------------------------------------------------------------------
301 -- | This function maps one exception into another as proposed in the
302 -- paper \"A semantics for imprecise exceptions\".
304 -- Notice that the usage of 'unsafePerformIO' is safe here.
306 mapException :: (Exception -> Exception) -> a -> a
307 mapException f v = unsafePerformIO (catch (evaluate v)
310 -----------------------------------------------------------------------------
311 -- 'try' and variations.
313 -- | Similar to 'catch', but returns an 'Either' result which is
314 -- @('Right' a)@ if no exception was raised, or @('Left' e)@ if an
315 -- exception was raised and its value is @e@.
317 -- > try a = catch (Right `liftM` a) (return . Left)
319 -- Note: as with 'catch', it is only polite to use this variant if you intend
320 -- to re-throw the exception after performing whatever cleanup is needed.
321 -- Otherwise, 'tryJust' is generally considered to be better.
323 -- Also note that "System.IO.Error" also exports a function called
324 -- 'System.IO.Error.try' with a similar type to 'Control.OldException.try',
325 -- except that it catches only the IO and user families of exceptions
326 -- (as required by the Haskell 98 @IO@ module).
328 try :: IO a -> IO (Either Exception a)
329 try a = catch (a >>= \ v -> return (Right v)) (\e -> return (Left e))
331 -- | A variant of 'try' that takes an exception predicate to select
332 -- which exceptions are caught (c.f. 'catchJust'). If the exception
333 -- does not match the predicate, it is re-thrown.
334 tryJust :: (Exception -> Maybe b) -> IO a -> IO (Either b a)
338 Right v -> return (Right v)
339 Left e -> case p e of
341 Just b -> return (Left b)
343 -----------------------------------------------------------------------------
344 -- Dynamic exceptions
347 -- #DynamicExceptions# Because the 'Exception' datatype is not extensible, there is an
348 -- interface for throwing and catching exceptions of type 'Dynamic'
349 -- (see "Data.Dynamic") which allows exception values of any type in
350 -- the 'Typeable' class to be thrown and caught.
352 -- | Raise any value as an exception, provided it is in the
354 throwDyn :: Typeable exception => exception -> b
356 throwDyn exception = throw (UserError "" "dynamic exception")
358 throwDyn exception = throw (DynException (toDyn exception))
361 #ifdef __GLASGOW_HASKELL__
362 -- | A variant of 'throwDyn' that throws the dynamic exception to an
363 -- arbitrary thread (GHC only: c.f. 'throwTo').
364 throwDynTo :: Typeable exception => ThreadId -> exception -> IO ()
365 throwDynTo t exception = New.throwTo t (DynException (toDyn exception))
366 #endif /* __GLASGOW_HASKELL__ */
368 -- | Catch dynamic exceptions of the required type. All other
369 -- exceptions are re-thrown, including dynamic exceptions of the wrong
372 -- When using dynamic exceptions it is advisable to define a new
373 -- datatype to use for your exception type, to avoid possible clashes
374 -- with dynamic exceptions used in other libraries.
376 catchDyn :: Typeable exception => IO a -> (exception -> IO a) -> IO a
378 catchDyn m k = m -- can't catch dyn exceptions in nhc98
380 catchDyn m k = New.catch m handler
381 where handler ex = case ex of
382 (DynException dyn) ->
383 case fromDynamic dyn of
384 Just exception -> k exception
389 -----------------------------------------------------------------------------
390 -- Exception Predicates
393 -- These pre-defined predicates may be used as the first argument to
394 -- 'catchJust', 'tryJust', or 'handleJust' to select certain common
395 -- classes of exceptions.
397 ioErrors :: Exception -> Maybe IOError
398 arithExceptions :: Exception -> Maybe New.ArithException
399 errorCalls :: Exception -> Maybe String
400 assertions :: Exception -> Maybe String
401 dynExceptions :: Exception -> Maybe Dynamic
402 asyncExceptions :: Exception -> Maybe New.AsyncException
403 userErrors :: Exception -> Maybe String
405 ioErrors (IOException e) = Just e
408 arithExceptions (ArithException e) = Just e
409 arithExceptions _ = Nothing
411 errorCalls (ErrorCall e) = Just e
412 errorCalls _ = Nothing
414 assertions (AssertionFailed e) = Just e
415 assertions _ = Nothing
417 dynExceptions (DynException e) = Just e
418 dynExceptions _ = Nothing
420 asyncExceptions (AsyncException e) = Just e
421 asyncExceptions _ = Nothing
423 userErrors (IOException e) | isUserError e = Just (ioeGetErrorString e)
424 userErrors _ = Nothing
426 -----------------------------------------------------------------------------
427 -- Some Useful Functions
429 -- | When you want to acquire a resource, do some work with it, and
430 -- then release the resource, it is a good idea to use 'bracket',
431 -- because 'bracket' will install the necessary exception handler to
432 -- release the resource in the event that an exception is raised
433 -- during the computation. If an exception is raised, then 'bracket' will
434 -- re-raise the exception (after performing the release).
436 -- A common example is opening a file:
439 -- > (openFile "filename" ReadMode)
441 -- > (\handle -> do { ... })
443 -- The arguments to 'bracket' are in this order so that we can partially apply
446 -- > withFile name mode = bracket (openFile name mode) hClose
450 :: IO a -- ^ computation to run first (\"acquire resource\")
451 -> (a -> IO b) -- ^ computation to run last (\"release resource\")
452 -> (a -> IO c) -- ^ computation to run in-between
453 -> IO c -- returns the value from the in-between computation
454 bracket before after thing =
455 mask $ \restore -> do
459 (\e -> do { _ <- after a; throw e })
464 -- | A specialised variant of 'bracket' with just a computation to run
467 finally :: IO a -- ^ computation to run first
468 -> IO b -- ^ computation to run afterward (even if an exception
470 -> IO a -- returns the value from the first computation
472 mask $ \restore -> do
475 (\e -> do { _ <- sequel; throw e })
479 -- | A variant of 'bracket' where the return value from the first computation
481 bracket_ :: IO a -> IO b -> IO c -> IO c
482 bracket_ before after thing = bracket before (const after) (const thing)
484 -- | Like bracket, but only performs the final action if there was an
485 -- exception raised by the in-between computation.
487 :: IO a -- ^ computation to run first (\"acquire resource\")
488 -> (a -> IO b) -- ^ computation to run last (\"release resource\")
489 -> (a -> IO c) -- ^ computation to run in-between
490 -> IO c -- returns the value from the in-between computation
491 bracketOnError before after thing =
492 mask $ \restore -> do
496 (\e -> do { _ <- after a; throw e })
498 -- -----------------------------------------------------------------------------
499 -- Asynchronous exceptions
503 #AsynchronousExceptions# Asynchronous exceptions are so-called because they arise due to
504 external influences, and can be raised at any point during execution.
505 'StackOverflow' and 'HeapOverflow' are two examples of
506 system-generated asynchronous exceptions.
508 The primary source of asynchronous exceptions, however, is
511 > throwTo :: ThreadId -> Exception -> IO ()
513 'throwTo' (also 'throwDynTo' and 'Control.Concurrent.killThread') allows one
514 running thread to raise an arbitrary exception in another thread. The
515 exception is therefore asynchronous with respect to the target thread,
516 which could be doing anything at the time it receives the exception.
517 Great care should be taken with asynchronous exceptions; it is all too
518 easy to introduce race conditions by the over zealous use of
523 There\'s an implied 'mask_' around every exception handler in a call
524 to one of the 'catch' family of functions. This is because that is
525 what you want most of the time - it eliminates a common race condition
526 in starting an exception handler, because there may be no exception
527 handler on the stack to handle another exception if one arrives
528 immediately. If asynchronous exceptions are blocked on entering the
529 handler, though, we have time to install a new exception handler
530 before being interrupted. If this weren\'t the default, one would have
531 to write something like
534 > catch (restore (...))
537 If you need to unblock asynchronous exceptions again in the exception
538 handler, just use 'unblock' as normal.
540 Note that 'try' and friends /do not/ have a similar default, because
541 there is no exception handler in this case. If you want to use 'try'
542 in an asynchronous-exception-safe way, you will need to use
548 Some operations are /interruptible/, which means that they can receive
549 asynchronous exceptions even in the scope of a 'mask'. Any function
550 which may itself block is defined as interruptible; this includes
551 'Control.Concurrent.MVar.takeMVar'
552 (but not 'Control.Concurrent.MVar.tryTakeMVar'),
553 and most operations which perform
554 some I\/O with the outside world. The reason for having
555 interruptible operations is so that we can write things like
557 > mask $ \restore -> do
559 > catch (restore (...))
562 if the 'Control.Concurrent.MVar.takeMVar' was not interruptible,
564 combination could lead to deadlock, because the thread itself would be
565 blocked in a state where it can\'t receive any asynchronous exceptions.
566 With 'Control.Concurrent.MVar.takeMVar' interruptible, however, we can be
567 safe in the knowledge that the thread can receive exceptions right up
568 until the point when the 'Control.Concurrent.MVar.takeMVar' succeeds.
569 Similar arguments apply for other interruptible operations like
570 'System.IO.openFile'.
573 #if !(__GLASGOW_HASKELL__ || __NHC__)
574 assert :: Bool -> a -> a
576 assert False _ = throw (AssertionFailed "")
580 #ifdef __GLASGOW_HASKELL__
581 {-# NOINLINE uncaughtExceptionHandler #-}
582 uncaughtExceptionHandler :: IORef (Exception -> IO ())
583 uncaughtExceptionHandler = unsafePerformIO (newIORef defaultHandler)
585 defaultHandler :: Exception -> IO ()
586 defaultHandler ex = do
587 (hFlush stdout) `New.catchAny` (\ _ -> return ())
589 Deadlock -> "no threads to run: infinite loop or deadlock?"
591 other -> showsPrec 0 other ""
592 withCString "%s" $ \cfmt ->
593 withCString msg $ \cmsg ->
596 -- don't use errorBelch() directly, because we cannot call varargs functions
598 foreign import ccall unsafe "HsBase.h errorBelch2"
599 errorBelch :: CString -> CString -> IO ()
601 setUncaughtExceptionHandler :: (Exception -> IO ()) -> IO ()
602 setUncaughtExceptionHandler = writeIORef uncaughtExceptionHandler
604 getUncaughtExceptionHandler :: IO (Exception -> IO ())
605 getUncaughtExceptionHandler = readIORef uncaughtExceptionHandler
608 -- ------------------------------------------------------------------------
609 -- Exception datatype and operations
611 -- |The type of exceptions. Every kind of system-generated exception
612 -- has a constructor in the 'Exception' type, and values of other
613 -- types may be injected into 'Exception' by coercing them to
614 -- 'Data.Dynamic.Dynamic' (see the section on Dynamic Exceptions:
615 -- "Control.OldException\#DynamicExceptions").
617 = ArithException New.ArithException
618 -- ^Exceptions raised by arithmetic
619 -- operations. (NOTE: GHC currently does not throw
620 -- 'ArithException's except for 'DivideByZero').
621 | ArrayException New.ArrayException
622 -- ^Exceptions raised by array-related
623 -- operations. (NOTE: GHC currently does not throw
624 -- 'ArrayException's).
625 | AssertionFailed String
626 -- ^This exception is thrown by the
627 -- 'assert' operation when the condition
628 -- fails. The 'String' argument contains the
629 -- location of the assertion in the source program.
630 | AsyncException New.AsyncException
631 -- ^Asynchronous exceptions (see section on Asynchronous Exceptions: "Control.OldException\#AsynchronousExceptions").
633 -- ^The current thread was executing a call to
634 -- 'Control.Concurrent.MVar.takeMVar' that could never return,
635 -- because there are no other references to this 'MVar'.
636 | BlockedIndefinitely
637 -- ^The current thread was waiting to retry an atomic memory transaction
638 -- that could never become possible to complete because there are no other
639 -- threads referring to any of the TVars involved.
641 -- ^The runtime detected an attempt to nest one STM transaction
642 -- inside another one, presumably due to the use of
643 -- 'unsafePeformIO' with 'atomically'.
645 -- ^There are no runnable threads, so the program is
646 -- deadlocked. The 'Deadlock' exception is
647 -- raised in the main thread only (see also: "Control.Concurrent").
648 | DynException Dynamic
649 -- ^Dynamically typed exceptions (see section on Dynamic Exceptions: "Control.OldException\#DynamicExceptions").
651 -- ^The 'ErrorCall' exception is thrown by 'error'. The 'String'
652 -- argument of 'ErrorCall' is the string passed to 'error' when it was
654 | ExitException New.ExitCode
655 -- ^The 'ExitException' exception is thrown by 'System.Exit.exitWith' (and
656 -- 'System.Exit.exitFailure'). The 'ExitCode' argument is the value passed
657 -- to 'System.Exit.exitWith'. An unhandled 'ExitException' exception in the
658 -- main thread will cause the program to be terminated with the given
660 | IOException New.IOException
661 -- ^These are the standard IO exceptions generated by
662 -- Haskell\'s @IO@ operations. See also "System.IO.Error".
663 | NoMethodError String
664 -- ^An attempt was made to invoke a class method which has
665 -- no definition in this instance, and there was no default
666 -- definition given in the class declaration. GHC issues a
667 -- warning when you compile an instance which has missing
670 -- ^The current thread is stuck in an infinite loop. This
671 -- exception may or may not be thrown when the program is
673 | PatternMatchFail String
674 -- ^A pattern matching failure. The 'String' argument should contain a
675 -- descriptive message including the function name, source file
678 -- ^An attempt was made to evaluate a field of a record
679 -- for which no value was given at construction time. The
680 -- 'String' argument gives the location of the
681 -- record construction in the source program.
683 -- ^A field selection was attempted on a constructor that
684 -- doesn\'t have the requested field. This can happen with
685 -- multi-constructor records when one or more fields are
686 -- missing from some of the constructors. The
687 -- 'String' argument gives the location of the
688 -- record selection in the source program.
690 -- ^An attempt was made to update a field in a record,
691 -- where the record doesn\'t have the requested field. This can
692 -- only occur with multi-constructor records, when one or more
693 -- fields are missing from some of the constructors. The
694 -- 'String' argument gives the location of the
695 -- record update in the source program.
696 INSTANCE_TYPEABLE0(Exception,exceptionTc,"Exception")
698 -- helper type for simplifying the type casting logic below
699 data Caster = forall e . New.Exception e => Caster (e -> Exception)
701 instance New.Exception Exception where
702 -- We need to collect all the sorts of exceptions that used to be
703 -- bundled up into the Exception type, and rebundle them for
705 fromException exc0 = foldr tryCast Nothing casters where
706 tryCast (Caster f) e = case fromException exc0 of
707 Just exc -> Just (f exc)
710 [Caster (\exc -> ArithException exc),
711 Caster (\exc -> ArrayException exc),
712 Caster (\(New.AssertionFailed err) -> AssertionFailed err),
713 Caster (\exc -> AsyncException exc),
714 Caster (\New.BlockedIndefinitelyOnMVar -> BlockedOnDeadMVar),
715 Caster (\New.BlockedIndefinitelyOnSTM -> BlockedIndefinitely),
716 Caster (\New.NestedAtomically -> NestedAtomically),
717 Caster (\New.Deadlock -> Deadlock),
718 Caster (\exc -> DynException exc),
719 Caster (\(New.ErrorCall err) -> ErrorCall err),
720 Caster (\exc -> ExitException exc),
721 Caster (\exc -> IOException exc),
722 Caster (\(New.NoMethodError err) -> NoMethodError err),
723 Caster (\New.NonTermination -> NonTermination),
724 Caster (\(New.PatternMatchFail err) -> PatternMatchFail err),
725 Caster (\(New.RecConError err) -> RecConError err),
726 Caster (\(New.RecSelError err) -> RecSelError err),
727 Caster (\(New.RecUpdError err) -> RecUpdError err),
728 -- Anything else gets taken as a Dynamic exception. It's
729 -- important that we put all exceptions into the old Exception
730 -- type somehow, or throwing a new exception wouldn't cause
731 -- the cleanup code for bracket, finally etc to happen.
732 Caster (\exc -> DynException (toDyn (exc :: New.SomeException)))]
734 -- Unbundle exceptions.
735 toException (ArithException exc) = toException exc
736 toException (ArrayException exc) = toException exc
737 toException (AssertionFailed err) = toException (New.AssertionFailed err)
738 toException (AsyncException exc) = toException exc
739 toException BlockedOnDeadMVar = toException New.BlockedIndefinitelyOnMVar
740 toException BlockedIndefinitely = toException New.BlockedIndefinitelyOnSTM
741 toException NestedAtomically = toException New.NestedAtomically
742 toException Deadlock = toException New.Deadlock
743 -- If a dynamic exception is a SomeException then resurrect it, so
744 -- that bracket, catch+throw etc rethrow the same exception even
745 -- when the exception is in the new style.
746 -- If it's not a SomeException, then just throw the Dynamic.
747 toException (DynException exc) = case fromDynamic exc of
749 Nothing -> toException exc
750 toException (ErrorCall err) = toException (New.ErrorCall err)
751 toException (ExitException exc) = toException exc
752 toException (IOException exc) = toException exc
753 toException (NoMethodError err) = toException (New.NoMethodError err)
754 toException NonTermination = toException New.NonTermination
755 toException (PatternMatchFail err) = toException (New.PatternMatchFail err)
756 toException (RecConError err) = toException (New.RecConError err)
757 toException (RecSelError err) = toException (New.RecSelError err)
758 toException (RecUpdError err) = toException (New.RecUpdError err)
760 instance Show Exception where
761 showsPrec _ (IOException err) = shows err
762 showsPrec _ (ArithException err) = shows err
763 showsPrec _ (ArrayException err) = shows err
764 showsPrec _ (ErrorCall err) = showString err
765 showsPrec _ (ExitException err) = showString "exit: " . shows err
766 showsPrec _ (NoMethodError err) = showString err
767 showsPrec _ (PatternMatchFail err) = showString err
768 showsPrec _ (RecSelError err) = showString err
769 showsPrec _ (RecConError err) = showString err
770 showsPrec _ (RecUpdError err) = showString err
771 showsPrec _ (AssertionFailed err) = showString err
772 showsPrec _ (DynException err) = showString "exception :: " . showsTypeRep (dynTypeRep err)
773 showsPrec _ (AsyncException e) = shows e
774 showsPrec p BlockedOnDeadMVar = showsPrec p New.BlockedIndefinitelyOnMVar
775 showsPrec p BlockedIndefinitely = showsPrec p New.BlockedIndefinitelyOnSTM
776 showsPrec p NestedAtomically = showsPrec p New.NestedAtomically
777 showsPrec p NonTermination = showsPrec p New.NonTermination
778 showsPrec p Deadlock = showsPrec p New.Deadlock
780 instance Eq Exception where
781 IOException e1 == IOException e2 = e1 == e2
782 ArithException e1 == ArithException e2 = e1 == e2
783 ArrayException e1 == ArrayException e2 = e1 == e2
784 ErrorCall e1 == ErrorCall e2 = e1 == e2
785 ExitException e1 == ExitException e2 = e1 == e2
786 NoMethodError e1 == NoMethodError e2 = e1 == e2
787 PatternMatchFail e1 == PatternMatchFail e2 = e1 == e2
788 RecSelError e1 == RecSelError e2 = e1 == e2
789 RecConError e1 == RecConError e2 = e1 == e2
790 RecUpdError e1 == RecUpdError e2 = e1 == e2
791 AssertionFailed e1 == AssertionFailed e2 = e1 == e2
792 DynException _ == DynException _ = False -- incomparable
793 AsyncException e1 == AsyncException e2 = e1 == e2
794 BlockedOnDeadMVar == BlockedOnDeadMVar = True
795 NonTermination == NonTermination = True
796 NestedAtomically == NestedAtomically = True
797 Deadlock == Deadlock = True