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 (
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.IOBase ( IO )
138 import qualified GHC.IOBase as ExceptionBase
139 import qualified GHC.IOBase 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.Handle ( stdout, hFlush )
148 import Prelude hiding (catch)
149 import Hugs.Prelude as New (ExitCode(..))
152 import qualified Control.Exception as New
153 import Control.Exception ( throw, SomeException(..), block, unblock, 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 ExceptionBase.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 handle
380 where handle 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 =
458 (\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
475 (\e -> do { sequel; throw e })
480 -- | A variant of 'bracket' where the return value from the first computation
482 bracket_ :: IO a -> IO b -> IO c -> IO c
483 bracket_ before after thing = bracket before (const after) (const thing)
485 -- | Like bracket, but only performs the final action if there was an
486 -- exception raised by the in-between computation.
488 :: IO a -- ^ computation to run first (\"acquire resource\")
489 -> (a -> IO b) -- ^ computation to run last (\"release resource\")
490 -> (a -> IO c) -- ^ computation to run in-between
491 -> IO c -- returns the value from the in-between computation
492 bracketOnError before after thing =
497 (\e -> do { after a; throw e })
500 -- -----------------------------------------------------------------------------
501 -- Asynchronous exceptions
505 #AsynchronousExceptions# Asynchronous exceptions are so-called because they arise due to
506 external influences, and can be raised at any point during execution.
507 'StackOverflow' and 'HeapOverflow' are two examples of
508 system-generated asynchronous exceptions.
510 The primary source of asynchronous exceptions, however, is
513 > throwTo :: ThreadId -> Exception -> IO ()
515 'throwTo' (also 'throwDynTo' and 'Control.Concurrent.killThread') allows one
516 running thread to raise an arbitrary exception in another thread. The
517 exception is therefore asynchronous with respect to the target thread,
518 which could be doing anything at the time it receives the exception.
519 Great care should be taken with asynchronous exceptions; it is all too
520 easy to introduce race conditions by the over zealous use of
525 There\'s an implied 'block' around every exception handler in a call
526 to one of the 'catch' family of functions. This is because that is
527 what you want most of the time - it eliminates a common race condition
528 in starting an exception handler, because there may be no exception
529 handler on the stack to handle another exception if one arrives
530 immediately. If asynchronous exceptions are blocked on entering the
531 handler, though, we have time to install a new exception handler
532 before being interrupted. If this weren\'t the default, one would have
533 to write something like
536 > catch (unblock (...))
540 If you need to unblock asynchronous exceptions again in the exception
541 handler, just use 'unblock' as normal.
543 Note that 'try' and friends /do not/ have a similar default, because
544 there is no exception handler in this case. If you want to use 'try'
545 in an asynchronous-exception-safe way, you will need to use
551 Some operations are /interruptible/, which means that they can receive
552 asynchronous exceptions even in the scope of a 'block'. Any function
553 which may itself block is defined as interruptible; this includes
554 'Control.Concurrent.MVar.takeMVar'
555 (but not 'Control.Concurrent.MVar.tryTakeMVar'),
556 and most operations which perform
557 some I\/O with the outside world. The reason for having
558 interruptible operations is so that we can write things like
562 > catch (unblock (...))
566 if the 'Control.Concurrent.MVar.takeMVar' was not interruptible,
568 combination could lead to deadlock, because the thread itself would be
569 blocked in a state where it can\'t receive any asynchronous exceptions.
570 With 'Control.Concurrent.MVar.takeMVar' interruptible, however, we can be
571 safe in the knowledge that the thread can receive exceptions right up
572 until the point when the 'Control.Concurrent.MVar.takeMVar' succeeds.
573 Similar arguments apply for other interruptible operations like
574 'System.IO.openFile'.
577 #if !(__GLASGOW_HASKELL__ || __NHC__)
578 assert :: Bool -> a -> a
580 assert False _ = throw (AssertionFailed "")
584 #ifdef __GLASGOW_HASKELL__
585 {-# NOINLINE uncaughtExceptionHandler #-}
586 uncaughtExceptionHandler :: IORef (Exception -> IO ())
587 uncaughtExceptionHandler = unsafePerformIO (newIORef defaultHandler)
589 defaultHandler :: Exception -> IO ()
590 defaultHandler ex = do
591 (hFlush stdout) `New.catchAny` (\ _ -> return ())
593 Deadlock -> "no threads to run: infinite loop or deadlock?"
595 other -> showsPrec 0 other ""
596 withCString "%s" $ \cfmt ->
597 withCString msg $ \cmsg ->
600 -- don't use errorBelch() directly, because we cannot call varargs functions
602 foreign import ccall unsafe "HsBase.h errorBelch2"
603 errorBelch :: CString -> CString -> IO ()
605 setUncaughtExceptionHandler :: (Exception -> IO ()) -> IO ()
606 setUncaughtExceptionHandler = writeIORef uncaughtExceptionHandler
608 getUncaughtExceptionHandler :: IO (Exception -> IO ())
609 getUncaughtExceptionHandler = readIORef uncaughtExceptionHandler
612 -- ------------------------------------------------------------------------
613 -- Exception datatype and operations
615 -- |The type of exceptions. Every kind of system-generated exception
616 -- has a constructor in the 'Exception' type, and values of other
617 -- types may be injected into 'Exception' by coercing them to
618 -- 'Data.Dynamic.Dynamic' (see the section on Dynamic Exceptions:
619 -- "Control.OldException\#DynamicExceptions").
621 = ArithException New.ArithException
622 -- ^Exceptions raised by arithmetic
623 -- operations. (NOTE: GHC currently does not throw
624 -- 'ArithException's except for 'DivideByZero').
625 | ArrayException New.ArrayException
626 -- ^Exceptions raised by array-related
627 -- operations. (NOTE: GHC currently does not throw
628 -- 'ArrayException's).
629 | AssertionFailed String
630 -- ^This exception is thrown by the
631 -- 'assert' operation when the condition
632 -- fails. The 'String' argument contains the
633 -- location of the assertion in the source program.
634 | AsyncException New.AsyncException
635 -- ^Asynchronous exceptions (see section on Asynchronous Exceptions: "Control.OldException\#AsynchronousExceptions").
637 -- ^The current thread was executing a call to
638 -- 'Control.Concurrent.MVar.takeMVar' that could never return,
639 -- because there are no other references to this 'MVar'.
640 | BlockedIndefinitely
641 -- ^The current thread was waiting to retry an atomic memory transaction
642 -- that could never become possible to complete because there are no other
643 -- threads referring to any of the TVars involved.
645 -- ^The runtime detected an attempt to nest one STM transaction
646 -- inside another one, presumably due to the use of
647 -- 'unsafePeformIO' with 'atomically'.
649 -- ^There are no runnable threads, so the program is
650 -- deadlocked. The 'Deadlock' exception is
651 -- raised in the main thread only (see also: "Control.Concurrent").
652 | DynException Dynamic
653 -- ^Dynamically typed exceptions (see section on Dynamic Exceptions: "Control.OldException\#DynamicExceptions").
655 -- ^The 'ErrorCall' exception is thrown by 'error'. The 'String'
656 -- argument of 'ErrorCall' is the string passed to 'error' when it was
658 | ExitException New.ExitCode
659 -- ^The 'ExitException' exception is thrown by 'System.Exit.exitWith' (and
660 -- 'System.Exit.exitFailure'). The 'ExitCode' argument is the value passed
661 -- to 'System.Exit.exitWith'. An unhandled 'ExitException' exception in the
662 -- main thread will cause the program to be terminated with the given
664 | IOException New.IOException
665 -- ^These are the standard IO exceptions generated by
666 -- Haskell\'s @IO@ operations. See also "System.IO.Error".
667 | NoMethodError String
668 -- ^An attempt was made to invoke a class method which has
669 -- no definition in this instance, and there was no default
670 -- definition given in the class declaration. GHC issues a
671 -- warning when you compile an instance which has missing
674 -- ^The current thread is stuck in an infinite loop. This
675 -- exception may or may not be thrown when the program is
677 | PatternMatchFail String
678 -- ^A pattern matching failure. The 'String' argument should contain a
679 -- descriptive message including the function name, source file
682 -- ^An attempt was made to evaluate a field of a record
683 -- for which no value was given at construction time. The
684 -- 'String' argument gives the location of the
685 -- record construction in the source program.
687 -- ^A field selection was attempted on a constructor that
688 -- doesn\'t have the requested field. This can happen with
689 -- multi-constructor records when one or more fields are
690 -- missing from some of the constructors. The
691 -- 'String' argument gives the location of the
692 -- record selection in the source program.
694 -- ^An attempt was made to update a field in a record,
695 -- where the record doesn\'t have the requested field. This can
696 -- only occur with multi-constructor records, when one or more
697 -- fields are missing from some of the constructors. The
698 -- 'String' argument gives the location of the
699 -- record update in the source program.
700 INSTANCE_TYPEABLE0(Exception,exceptionTc,"Exception")
702 nonTermination :: SomeException
703 nonTermination = New.toException NonTermination
705 -- helper type for simplifying the type casting logic below
706 data Caster = forall e . ExceptionBase.Exception e => Caster (e -> Exception)
708 instance New.Exception Exception where
709 -- We need to collect all the sorts of exceptions that used to be
710 -- bundled up into the Exception type, and rebundle them for
712 fromException (SomeException exc) = foldr tryCast Nothing casters where
713 tryCast (Caster f) e = case cast exc of
714 Just exc -> Just (f exc)
718 Caster (\exc -> ArithException exc),
719 Caster (\exc -> ArrayException exc),
720 Caster (\(New.AssertionFailed err) -> AssertionFailed err),
721 Caster (\exc -> AsyncException exc),
722 Caster (\New.BlockedOnDeadMVar -> BlockedOnDeadMVar),
723 Caster (\New.BlockedIndefinitely -> BlockedIndefinitely),
724 Caster (\New.NestedAtomically -> NestedAtomically),
725 Caster (\New.Deadlock -> Deadlock),
726 Caster (\exc -> DynException exc),
727 Caster (\(New.ErrorCall err) -> ErrorCall err),
728 Caster (\exc -> ExitException exc),
729 Caster (\exc -> IOException exc),
730 Caster (\(New.NoMethodError err) -> NoMethodError err),
731 Caster (\New.NonTermination -> NonTermination),
732 Caster (\(New.PatternMatchFail err) -> PatternMatchFail err),
733 Caster (\(New.RecConError err) -> RecConError err),
734 Caster (\(New.RecSelError err) -> RecSelError err),
735 Caster (\(New.RecUpdError err) -> RecUpdError err)]
737 -- Unbundle exceptions.
738 toException (ArithException exc) = SomeException exc
739 toException (ArrayException exc) = SomeException exc
740 toException (AssertionFailed err) = SomeException (New.AssertionFailed err)
741 toException (AsyncException exc) = SomeException exc
742 toException BlockedOnDeadMVar = SomeException New.BlockedOnDeadMVar
743 toException BlockedIndefinitely = SomeException New.BlockedIndefinitely
744 toException NestedAtomically = SomeException New.NestedAtomically
745 toException Deadlock = SomeException New.Deadlock
746 toException (DynException exc) = SomeException exc
747 toException (ErrorCall err) = SomeException (New.ErrorCall err)
748 toException (ExitException exc) = SomeException exc
749 toException (IOException exc) = SomeException exc
750 toException (NoMethodError err) = SomeException (New.NoMethodError err)
751 toException NonTermination = SomeException New.NonTermination
752 toException (PatternMatchFail err) = SomeException (New.PatternMatchFail err)
753 toException (RecConError err) = SomeException (New.RecConError err)
754 toException (RecSelError err) = SomeException (New.RecSelError err)
755 toException (RecUpdError err) = SomeException (New.RecUpdError err)
757 instance Show Exception where
758 showsPrec _ (IOException err) = shows err
759 showsPrec _ (ArithException err) = shows err
760 showsPrec _ (ArrayException err) = shows err
761 showsPrec _ (ErrorCall err) = showString err
762 showsPrec _ (ExitException err) = showString "exit: " . shows err
763 showsPrec _ (NoMethodError err) = showString err
764 showsPrec _ (PatternMatchFail err) = showString err
765 showsPrec _ (RecSelError err) = showString err
766 showsPrec _ (RecConError err) = showString err
767 showsPrec _ (RecUpdError err) = showString err
768 showsPrec _ (AssertionFailed err) = showString err
769 showsPrec _ (DynException err) = showString "exception :: " . showsTypeRep (dynTypeRep err)
770 showsPrec _ (AsyncException e) = shows e
771 showsPrec p BlockedOnDeadMVar = showsPrec p New.BlockedOnDeadMVar
772 showsPrec p BlockedIndefinitely = showsPrec p New.BlockedIndefinitely
773 showsPrec p NestedAtomically = showsPrec p New.NestedAtomically
774 showsPrec p NonTermination = showsPrec p New.NonTermination
775 showsPrec p Deadlock = showsPrec p New.Deadlock
777 instance Eq Exception where
778 IOException e1 == IOException e2 = e1 == e2
779 ArithException e1 == ArithException e2 = e1 == e2
780 ArrayException e1 == ArrayException e2 = e1 == e2
781 ErrorCall e1 == ErrorCall e2 = e1 == e2
782 ExitException e1 == ExitException e2 = e1 == e2
783 NoMethodError e1 == NoMethodError e2 = e1 == e2
784 PatternMatchFail e1 == PatternMatchFail e2 = e1 == e2
785 RecSelError e1 == RecSelError e2 = e1 == e2
786 RecConError e1 == RecConError e2 = e1 == e2
787 RecUpdError e1 == RecUpdError e2 = e1 == e2
788 AssertionFailed e1 == AssertionFailed e2 = e1 == e2
789 DynException _ == DynException _ = False -- incomparable
790 AsyncException e1 == AsyncException e2 = e1 == e2
791 BlockedOnDeadMVar == BlockedOnDeadMVar = True
792 NonTermination == NonTermination = True
793 NestedAtomically == NestedAtomically = True
794 Deadlock == Deadlock = True