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__
136 -- import GHC.IO ( IO )
137 import GHC.IO.Handle.FD ( stdout )
138 import qualified GHC.IO as New
139 import qualified GHC.IO.Exception as New
140 import GHC.Conc hiding (setUncaughtExceptionHandler,
141 getUncaughtExceptionHandler)
142 import Data.IORef ( IORef, newIORef, readIORef, writeIORef )
143 import Foreign.C.String ( CString, withCString )
144 import GHC.IO.Handle ( hFlush )
148 import Prelude hiding (catch)
149 import Hugs.Prelude as New (ExitCode(..))
152 import qualified Control.Exception as New
153 import Control.Exception ( toException, fromException, throw, block, unblock, mask, evaluate, throwIO )
154 import System.IO.Error hiding ( catch, try )
155 import System.IO.Unsafe (unsafePerformIO)
161 import System.IO.Error (catch, ioError)
163 import DIOError -- defn of IOError type
165 -- minimum needed for nhc98 to pretend it has Exceptions
166 type Exception = IOError
167 type IOException = IOError
172 throwIO :: Exception -> IO a
174 throw :: Exception -> a
175 throw = unsafePerformIO . throwIO
177 evaluate :: a -> IO a
178 evaluate x = x `seq` return x
180 ioErrors :: Exception -> Maybe IOError
182 arithExceptions :: Exception -> Maybe ArithException
183 arithExceptions = const Nothing
184 errorCalls :: Exception -> Maybe String
185 errorCalls = const Nothing
186 dynExceptions :: Exception -> Maybe Dynamic
187 dynExceptions = const Nothing
188 assertions :: Exception -> Maybe String
189 assertions = const Nothing
190 asyncExceptions :: Exception -> Maybe AsyncException
191 asyncExceptions = const Nothing
192 userErrors :: Exception -> Maybe String
193 userErrors (UserError _ s) = Just s
194 userErrors _ = Nothing
196 block :: IO a -> IO a
198 unblock :: IO a -> IO a
201 assert :: Bool -> a -> a
203 assert False _ = throw (UserError "" "Assertion failed")
206 -----------------------------------------------------------------------------
207 -- Catching exceptions
209 -- |This is the simplest of the exception-catching functions. It
210 -- takes a single argument, runs it, and if an exception is raised
211 -- the \"handler\" is executed, with the value of the exception passed as an
212 -- argument. Otherwise, the result is returned as normal. For example:
214 -- > catch (openFile f ReadMode)
215 -- > (\e -> hPutStr stderr ("Couldn't open "++f++": " ++ show e))
217 -- For catching exceptions in pure (non-'IO') expressions, see the
218 -- function 'evaluate'.
220 -- Note that due to Haskell\'s unspecified evaluation order, an
221 -- expression may return one of several possible exceptions: consider
222 -- the expression @error \"urk\" + 1 \`div\` 0@. Does
223 -- 'catch' execute the handler passing
224 -- @ErrorCall \"urk\"@, or @ArithError DivideByZero@?
226 -- The answer is \"either\": 'catch' makes a
227 -- non-deterministic choice about which exception to catch. If you
228 -- call it again, you might get a different exception back. This is
229 -- ok, because 'catch' is an 'IO' computation.
231 -- Note that 'catch' catches all types of exceptions, and is generally
232 -- used for \"cleaning up\" before passing on the exception using
233 -- 'throwIO'. It is not good practice to discard the exception and
234 -- continue, without first checking the type of the exception (it
235 -- might be a 'ThreadKilled', for example). In this case it is usually better
236 -- to use 'catchJust' and select the kinds of exceptions to catch.
238 -- Also note that the "Prelude" also exports a function called
239 -- 'Prelude.catch' with a similar type to 'Control.OldException.catch',
240 -- except that the "Prelude" version only catches the IO and user
241 -- families of exceptions (as required by Haskell 98).
243 -- We recommend either hiding the "Prelude" version of 'Prelude.catch'
244 -- when importing "Control.OldException":
246 -- > import Prelude hiding (catch)
248 -- or importing "Control.OldException" qualified, to avoid name-clashes:
250 -- > import qualified Control.OldException as C
252 -- and then using @C.catch@
255 catch :: IO a -- ^ The computation to run
256 -> (Exception -> IO a) -- ^ Handler to invoke if an exception is raised
258 -- note: bundling the exceptions is done in the New.Exception
259 -- instance of Exception; see below.
262 -- | The function 'catchJust' is like 'catch', but it takes an extra
263 -- argument which is an /exception predicate/, a function which
264 -- selects which type of exceptions we\'re interested in. There are
265 -- some predefined exception predicates for useful subsets of
266 -- exceptions: 'ioErrors', 'arithExceptions', and so on. For example,
267 -- to catch just calls to the 'error' function, we could use
269 -- > result <- catchJust errorCalls thing_to_try handler
271 -- Any other exceptions which are not matched by the predicate
272 -- are re-raised, and may be caught by an enclosing
273 -- 'catch' or 'catchJust'.
275 :: (Exception -> Maybe b) -- ^ Predicate to select exceptions
276 -> IO a -- ^ Computation to run
277 -> (b -> IO a) -- ^ Handler
279 catchJust p a handler = catch a handler'
280 where handler' e = case p e of
284 -- | A version of 'catch' with the arguments swapped around; useful in
285 -- situations where the code for the handler is shorter. For example:
287 -- > do handle (\e -> exitWith (ExitFailure 1)) $
289 handle :: (Exception -> IO a) -> IO a -> IO a
292 -- | A version of 'catchJust' with the arguments swapped around (see
294 handleJust :: (Exception -> Maybe b) -> (b -> IO a) -> IO a -> IO a
295 handleJust p = flip (catchJust p)
297 -----------------------------------------------------------------------------
300 -- | This function maps one exception into another as proposed in the
301 -- paper \"A semantics for imprecise exceptions\".
303 -- Notice that the usage of 'unsafePerformIO' is safe here.
305 mapException :: (Exception -> Exception) -> a -> a
306 mapException f v = unsafePerformIO (catch (evaluate v)
309 -----------------------------------------------------------------------------
310 -- 'try' and variations.
312 -- | Similar to 'catch', but returns an 'Either' result which is
313 -- @('Right' a)@ if no exception was raised, or @('Left' e)@ if an
314 -- exception was raised and its value is @e@.
316 -- > try a = catch (Right `liftM` a) (return . Left)
318 -- Note: as with 'catch', it is only polite to use this variant if you intend
319 -- to re-throw the exception after performing whatever cleanup is needed.
320 -- Otherwise, 'tryJust' is generally considered to be better.
322 -- Also note that "System.IO.Error" also exports a function called
323 -- 'System.IO.Error.try' with a similar type to 'Control.OldException.try',
324 -- except that it catches only the IO and user families of exceptions
325 -- (as required by the Haskell 98 @IO@ module).
327 try :: IO a -> IO (Either Exception a)
328 try a = catch (a >>= \ v -> return (Right v)) (\e -> return (Left e))
330 -- | A variant of 'try' that takes an exception predicate to select
331 -- which exceptions are caught (c.f. 'catchJust'). If the exception
332 -- does not match the predicate, it is re-thrown.
333 tryJust :: (Exception -> Maybe b) -> IO a -> IO (Either b a)
337 Right v -> return (Right v)
338 Left e -> case p e of
340 Just b -> return (Left b)
342 -----------------------------------------------------------------------------
343 -- Dynamic exceptions
346 -- #DynamicExceptions# Because the 'Exception' datatype is not extensible, there is an
347 -- interface for throwing and catching exceptions of type 'Dynamic'
348 -- (see "Data.Dynamic") which allows exception values of any type in
349 -- the 'Typeable' class to be thrown and caught.
351 -- | Raise any value as an exception, provided it is in the
353 throwDyn :: Typeable exception => exception -> b
355 throwDyn exception = throw (UserError "" "dynamic exception")
357 throwDyn exception = throw (DynException (toDyn exception))
360 #ifdef __GLASGOW_HASKELL__
361 -- | A variant of 'throwDyn' that throws the dynamic exception to an
362 -- arbitrary thread (GHC only: c.f. 'throwTo').
363 throwDynTo :: Typeable exception => ThreadId -> exception -> IO ()
364 throwDynTo t exception = New.throwTo t (DynException (toDyn exception))
365 #endif /* __GLASGOW_HASKELL__ */
367 -- | Catch dynamic exceptions of the required type. All other
368 -- exceptions are re-thrown, including dynamic exceptions of the wrong
371 -- When using dynamic exceptions it is advisable to define a new
372 -- datatype to use for your exception type, to avoid possible clashes
373 -- with dynamic exceptions used in other libraries.
375 catchDyn :: Typeable exception => IO a -> (exception -> IO a) -> IO a
377 catchDyn m k = m -- can't catch dyn exceptions in nhc98
379 catchDyn m k = New.catch m handler
380 where handler ex = case ex of
381 (DynException dyn) ->
382 case fromDynamic dyn of
383 Just exception -> k exception
388 -----------------------------------------------------------------------------
389 -- Exception Predicates
392 -- These pre-defined predicates may be used as the first argument to
393 -- 'catchJust', 'tryJust', or 'handleJust' to select certain common
394 -- classes of exceptions.
396 ioErrors :: Exception -> Maybe IOError
397 arithExceptions :: Exception -> Maybe New.ArithException
398 errorCalls :: Exception -> Maybe String
399 assertions :: Exception -> Maybe String
400 dynExceptions :: Exception -> Maybe Dynamic
401 asyncExceptions :: Exception -> Maybe New.AsyncException
402 userErrors :: Exception -> Maybe String
404 ioErrors (IOException e) = Just e
407 arithExceptions (ArithException e) = Just e
408 arithExceptions _ = Nothing
410 errorCalls (ErrorCall e) = Just e
411 errorCalls _ = Nothing
413 assertions (AssertionFailed e) = Just e
414 assertions _ = Nothing
416 dynExceptions (DynException e) = Just e
417 dynExceptions _ = Nothing
419 asyncExceptions (AsyncException e) = Just e
420 asyncExceptions _ = Nothing
422 userErrors (IOException e) | isUserError e = Just (ioeGetErrorString e)
423 userErrors _ = Nothing
425 -----------------------------------------------------------------------------
426 -- Some Useful Functions
428 -- | When you want to acquire a resource, do some work with it, and
429 -- then release the resource, it is a good idea to use 'bracket',
430 -- because 'bracket' will install the necessary exception handler to
431 -- release the resource in the event that an exception is raised
432 -- during the computation. If an exception is raised, then 'bracket' will
433 -- re-raise the exception (after performing the release).
435 -- A common example is opening a file:
438 -- > (openFile "filename" ReadMode)
440 -- > (\handle -> do { ... })
442 -- The arguments to 'bracket' are in this order so that we can partially apply
445 -- > withFile name mode = bracket (openFile name mode) hClose
449 :: IO a -- ^ computation to run first (\"acquire resource\")
450 -> (a -> IO b) -- ^ computation to run last (\"release resource\")
451 -> (a -> IO c) -- ^ computation to run in-between
452 -> IO c -- returns the value from the in-between computation
453 bracket before after thing =
454 mask $ \restore -> do
458 (\e -> do { _ <- after a; throw e })
463 -- | A specialised variant of 'bracket' with just a computation to run
466 finally :: IO a -- ^ computation to run first
467 -> IO b -- ^ computation to run afterward (even if an exception
469 -> IO a -- returns the value from the first computation
471 mask $ \restore -> do
474 (\e -> do { _ <- sequel; throw e })
478 -- | A variant of 'bracket' where the return value from the first computation
480 bracket_ :: IO a -> IO b -> IO c -> IO c
481 bracket_ before after thing = bracket before (const after) (const thing)
483 -- | Like bracket, but only performs the final action if there was an
484 -- exception raised by the in-between computation.
486 :: IO a -- ^ computation to run first (\"acquire resource\")
487 -> (a -> IO b) -- ^ computation to run last (\"release resource\")
488 -> (a -> IO c) -- ^ computation to run in-between
489 -> IO c -- returns the value from the in-between computation
490 bracketOnError before after thing =
491 mask $ \restore -> do
495 (\e -> do { _ <- after a; throw e })
497 -- -----------------------------------------------------------------------------
498 -- Asynchronous exceptions
502 #AsynchronousExceptions# Asynchronous exceptions are so-called because they arise due to
503 external influences, and can be raised at any point during execution.
504 'StackOverflow' and 'HeapOverflow' are two examples of
505 system-generated asynchronous exceptions.
507 The primary source of asynchronous exceptions, however, is
510 > throwTo :: ThreadId -> Exception -> IO ()
512 'throwTo' (also 'throwDynTo' and 'Control.Concurrent.killThread') allows one
513 running thread to raise an arbitrary exception in another thread. The
514 exception is therefore asynchronous with respect to the target thread,
515 which could be doing anything at the time it receives the exception.
516 Great care should be taken with asynchronous exceptions; it is all too
517 easy to introduce race conditions by the over zealous use of
522 There\'s an implied 'mask_' around every exception handler in a call
523 to one of the 'catch' family of functions. This is because that is
524 what you want most of the time - it eliminates a common race condition
525 in starting an exception handler, because there may be no exception
526 handler on the stack to handle another exception if one arrives
527 immediately. If asynchronous exceptions are blocked on entering the
528 handler, though, we have time to install a new exception handler
529 before being interrupted. If this weren\'t the default, one would have
530 to write something like
533 > catch (restore (...))
536 If you need to unblock asynchronous exceptions again in the exception
537 handler, just use 'unblock' as normal.
539 Note that 'try' and friends /do not/ have a similar default, because
540 there is no exception handler in this case. If you want to use 'try'
541 in an asynchronous-exception-safe way, you will need to use
547 Some operations are /interruptible/, which means that they can receive
548 asynchronous exceptions even in the scope of a 'mask'. Any function
549 which may itself block is defined as interruptible; this includes
550 'Control.Concurrent.MVar.takeMVar'
551 (but not 'Control.Concurrent.MVar.tryTakeMVar'),
552 and most operations which perform
553 some I\/O with the outside world. The reason for having
554 interruptible operations is so that we can write things like
556 > mask $ \restore -> do
558 > catch (restore (...))
561 if the 'Control.Concurrent.MVar.takeMVar' was not interruptible,
563 combination could lead to deadlock, because the thread itself would be
564 blocked in a state where it can\'t receive any asynchronous exceptions.
565 With 'Control.Concurrent.MVar.takeMVar' interruptible, however, we can be
566 safe in the knowledge that the thread can receive exceptions right up
567 until the point when the 'Control.Concurrent.MVar.takeMVar' succeeds.
568 Similar arguments apply for other interruptible operations like
569 'System.IO.openFile'.
572 #if !(__GLASGOW_HASKELL__ || __NHC__)
573 assert :: Bool -> a -> a
575 assert False _ = throw (AssertionFailed "")
579 #ifdef __GLASGOW_HASKELL__
580 {-# NOINLINE uncaughtExceptionHandler #-}
581 uncaughtExceptionHandler :: IORef (Exception -> IO ())
582 uncaughtExceptionHandler = unsafePerformIO (newIORef defaultHandler)
584 defaultHandler :: Exception -> IO ()
585 defaultHandler ex = do
586 (hFlush stdout) `New.catchAny` (\ _ -> return ())
588 Deadlock -> "no threads to run: infinite loop or deadlock?"
590 other -> showsPrec 0 other ""
591 withCString "%s" $ \cfmt ->
592 withCString msg $ \cmsg ->
595 -- don't use errorBelch() directly, because we cannot call varargs functions
597 foreign import ccall unsafe "HsBase.h errorBelch2"
598 errorBelch :: CString -> CString -> IO ()
600 setUncaughtExceptionHandler :: (Exception -> IO ()) -> IO ()
601 setUncaughtExceptionHandler = writeIORef uncaughtExceptionHandler
603 getUncaughtExceptionHandler :: IO (Exception -> IO ())
604 getUncaughtExceptionHandler = readIORef uncaughtExceptionHandler
607 -- ------------------------------------------------------------------------
608 -- Exception datatype and operations
610 -- |The type of exceptions. Every kind of system-generated exception
611 -- has a constructor in the 'Exception' type, and values of other
612 -- types may be injected into 'Exception' by coercing them to
613 -- 'Data.Dynamic.Dynamic' (see the section on Dynamic Exceptions:
614 -- "Control.OldException\#DynamicExceptions").
616 = ArithException New.ArithException
617 -- ^Exceptions raised by arithmetic
618 -- operations. (NOTE: GHC currently does not throw
619 -- 'ArithException's except for 'DivideByZero').
620 | ArrayException New.ArrayException
621 -- ^Exceptions raised by array-related
622 -- operations. (NOTE: GHC currently does not throw
623 -- 'ArrayException's).
624 | AssertionFailed String
625 -- ^This exception is thrown by the
626 -- 'assert' operation when the condition
627 -- fails. The 'String' argument contains the
628 -- location of the assertion in the source program.
629 | AsyncException New.AsyncException
630 -- ^Asynchronous exceptions (see section on Asynchronous Exceptions: "Control.OldException\#AsynchronousExceptions").
632 -- ^The current thread was executing a call to
633 -- 'Control.Concurrent.MVar.takeMVar' that could never return,
634 -- because there are no other references to this 'MVar'.
635 | BlockedIndefinitely
636 -- ^The current thread was waiting to retry an atomic memory transaction
637 -- that could never become possible to complete because there are no other
638 -- threads referring to any of the TVars involved.
640 -- ^The runtime detected an attempt to nest one STM transaction
641 -- inside another one, presumably due to the use of
642 -- 'unsafePeformIO' with 'atomically'.
644 -- ^There are no runnable threads, so the program is
645 -- deadlocked. The 'Deadlock' exception is
646 -- raised in the main thread only (see also: "Control.Concurrent").
647 | DynException Dynamic
648 -- ^Dynamically typed exceptions (see section on Dynamic Exceptions: "Control.OldException\#DynamicExceptions").
650 -- ^The 'ErrorCall' exception is thrown by 'error'. The 'String'
651 -- argument of 'ErrorCall' is the string passed to 'error' when it was
653 | ExitException New.ExitCode
654 -- ^The 'ExitException' exception is thrown by 'System.Exit.exitWith' (and
655 -- 'System.Exit.exitFailure'). The 'ExitCode' argument is the value passed
656 -- to 'System.Exit.exitWith'. An unhandled 'ExitException' exception in the
657 -- main thread will cause the program to be terminated with the given
659 | IOException New.IOException
660 -- ^These are the standard IO exceptions generated by
661 -- Haskell\'s @IO@ operations. See also "System.IO.Error".
662 | NoMethodError String
663 -- ^An attempt was made to invoke a class method which has
664 -- no definition in this instance, and there was no default
665 -- definition given in the class declaration. GHC issues a
666 -- warning when you compile an instance which has missing
669 -- ^The current thread is stuck in an infinite loop. This
670 -- exception may or may not be thrown when the program is
672 | PatternMatchFail String
673 -- ^A pattern matching failure. The 'String' argument should contain a
674 -- descriptive message including the function name, source file
677 -- ^An attempt was made to evaluate a field of a record
678 -- for which no value was given at construction time. The
679 -- 'String' argument gives the location of the
680 -- record construction in the source program.
682 -- ^A field selection was attempted on a constructor that
683 -- doesn\'t have the requested field. This can happen with
684 -- multi-constructor records when one or more fields are
685 -- missing from some of the constructors. The
686 -- 'String' argument gives the location of the
687 -- record selection in the source program.
689 -- ^An attempt was made to update a field in a record,
690 -- where the record doesn\'t have the requested field. This can
691 -- only occur with multi-constructor records, when one or more
692 -- fields are missing from some of the constructors. The
693 -- 'String' argument gives the location of the
694 -- record update in the source program.
695 INSTANCE_TYPEABLE0(Exception,exceptionTc,"Exception")
697 -- helper type for simplifying the type casting logic below
698 data Caster = forall e . New.Exception e => Caster (e -> Exception)
700 instance New.Exception Exception where
701 -- We need to collect all the sorts of exceptions that used to be
702 -- bundled up into the Exception type, and rebundle them for
704 fromException exc0 = foldr tryCast Nothing casters where
705 tryCast (Caster f) e = case fromException exc0 of
706 Just exc -> Just (f exc)
709 [Caster (\exc -> ArithException exc),
710 Caster (\exc -> ArrayException exc),
711 Caster (\(New.AssertionFailed err) -> AssertionFailed err),
712 Caster (\exc -> AsyncException exc),
713 Caster (\New.BlockedIndefinitelyOnMVar -> BlockedOnDeadMVar),
714 Caster (\New.BlockedIndefinitelyOnSTM -> BlockedIndefinitely),
715 Caster (\New.NestedAtomically -> NestedAtomically),
716 Caster (\New.Deadlock -> Deadlock),
717 Caster (\exc -> DynException exc),
718 Caster (\(New.ErrorCall err) -> ErrorCall err),
719 Caster (\exc -> ExitException exc),
720 Caster (\exc -> IOException exc),
721 Caster (\(New.NoMethodError err) -> NoMethodError err),
722 Caster (\New.NonTermination -> NonTermination),
723 Caster (\(New.PatternMatchFail err) -> PatternMatchFail err),
724 Caster (\(New.RecConError err) -> RecConError err),
725 Caster (\(New.RecSelError err) -> RecSelError err),
726 Caster (\(New.RecUpdError err) -> RecUpdError err),
727 -- Anything else gets taken as a Dynamic exception. It's
728 -- important that we put all exceptions into the old Exception
729 -- type somehow, or throwing a new exception wouldn't cause
730 -- the cleanup code for bracket, finally etc to happen.
731 Caster (\exc -> DynException (toDyn (exc :: New.SomeException)))]
733 -- Unbundle exceptions.
734 toException (ArithException exc) = toException exc
735 toException (ArrayException exc) = toException exc
736 toException (AssertionFailed err) = toException (New.AssertionFailed err)
737 toException (AsyncException exc) = toException exc
738 toException BlockedOnDeadMVar = toException New.BlockedIndefinitelyOnMVar
739 toException BlockedIndefinitely = toException New.BlockedIndefinitelyOnSTM
740 toException NestedAtomically = toException New.NestedAtomically
741 toException Deadlock = toException New.Deadlock
742 -- If a dynamic exception is a SomeException then resurrect it, so
743 -- that bracket, catch+throw etc rethrow the same exception even
744 -- when the exception is in the new style.
745 -- If it's not a SomeException, then just throw the Dynamic.
746 toException (DynException exc) = case fromDynamic exc of
748 Nothing -> toException exc
749 toException (ErrorCall err) = toException (New.ErrorCall err)
750 toException (ExitException exc) = toException exc
751 toException (IOException exc) = toException exc
752 toException (NoMethodError err) = toException (New.NoMethodError err)
753 toException NonTermination = toException New.NonTermination
754 toException (PatternMatchFail err) = toException (New.PatternMatchFail err)
755 toException (RecConError err) = toException (New.RecConError err)
756 toException (RecSelError err) = toException (New.RecSelError err)
757 toException (RecUpdError err) = toException (New.RecUpdError err)
759 instance Show Exception where
760 showsPrec _ (IOException err) = shows err
761 showsPrec _ (ArithException err) = shows err
762 showsPrec _ (ArrayException err) = shows err
763 showsPrec _ (ErrorCall err) = showString err
764 showsPrec _ (ExitException err) = showString "exit: " . shows err
765 showsPrec _ (NoMethodError err) = showString err
766 showsPrec _ (PatternMatchFail err) = showString err
767 showsPrec _ (RecSelError err) = showString err
768 showsPrec _ (RecConError err) = showString err
769 showsPrec _ (RecUpdError err) = showString err
770 showsPrec _ (AssertionFailed err) = showString err
771 showsPrec _ (DynException err) = showString "exception :: " . showsTypeRep (dynTypeRep err)
772 showsPrec _ (AsyncException e) = shows e
773 showsPrec p BlockedOnDeadMVar = showsPrec p New.BlockedIndefinitelyOnMVar
774 showsPrec p BlockedIndefinitely = showsPrec p New.BlockedIndefinitelyOnSTM
775 showsPrec p NestedAtomically = showsPrec p New.NestedAtomically
776 showsPrec p NonTermination = showsPrec p New.NonTermination
777 showsPrec p Deadlock = showsPrec p New.Deadlock
779 instance Eq Exception where
780 IOException e1 == IOException e2 = e1 == e2
781 ArithException e1 == ArithException e2 = e1 == e2
782 ArrayException e1 == ArrayException e2 = e1 == e2
783 ErrorCall e1 == ErrorCall e2 = e1 == e2
784 ExitException e1 == ExitException e2 = e1 == e2
785 NoMethodError e1 == NoMethodError e2 = e1 == e2
786 PatternMatchFail e1 == PatternMatchFail e2 = e1 == e2
787 RecSelError e1 == RecSelError e2 = e1 == e2
788 RecConError e1 == RecConError e2 = e1 == e2
789 RecUpdError e1 == RecUpdError e2 = e1 == e2
790 AssertionFailed e1 == AssertionFailed e2 = e1 == e2
791 DynException _ == DynException _ = False -- incomparable
792 AsyncException e1 == AsyncException e2 = e1 == e2
793 BlockedOnDeadMVar == BlockedOnDeadMVar = True
794 NonTermination == NonTermination = True
795 NestedAtomically == NestedAtomically = True
796 Deadlock == Deadlock = True