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 GHC.IOBase (block, unblock, evaluate, catchException, throwIO)
139 import qualified GHC.IOBase as ExceptionBase
140 import qualified GHC.IOBase 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.Handle ( stdout, hFlush )
149 import Hugs.Exception as ExceptionBase
152 import qualified Control.Exception as New
153 import Control.Exception ( throw, SomeException )
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
259 -- We need to catch all the sorts of exceptions that used to be
260 -- bundled up into the Exception type, and rebundle them for the
261 -- legacy handler we've been given.
263 [New.Handler (\e -> handler e),
264 New.Handler (\exc -> handler (ArithException exc)),
265 New.Handler (\exc -> handler (ArrayException exc)),
266 New.Handler (\(New.AssertionFailed err) -> handler (AssertionFailed err)),
267 New.Handler (\exc -> handler (AsyncException exc)),
268 New.Handler (\New.BlockedOnDeadMVar -> handler BlockedOnDeadMVar),
269 New.Handler (\New.BlockedIndefinitely -> handler BlockedIndefinitely),
270 New.Handler (\New.NestedAtomically -> handler NestedAtomically),
271 New.Handler (\New.Deadlock -> handler Deadlock),
272 New.Handler (\exc -> handler (DynException exc)),
273 New.Handler (\(New.ErrorCall err) -> handler (ErrorCall err)),
274 New.Handler (\exc -> handler (ExitException exc)),
275 New.Handler (\exc -> handler (IOException exc)),
276 New.Handler (\(New.NoMethodError err) -> handler (NoMethodError err)),
277 New.Handler (\New.NonTermination -> handler NonTermination),
278 New.Handler (\(New.PatternMatchFail err) -> handler (PatternMatchFail err)),
279 New.Handler (\(New.RecConError err) -> handler (RecConError err)),
280 New.Handler (\(New.RecSelError err) -> handler (RecSelError err)),
281 New.Handler (\(New.RecUpdError err) -> handler (RecUpdError err))]
283 -- | The function 'catchJust' is like 'catch', but it takes an extra
284 -- argument which is an /exception predicate/, a function which
285 -- selects which type of exceptions we\'re interested in. There are
286 -- some predefined exception predicates for useful subsets of
287 -- exceptions: 'ioErrors', 'arithExceptions', and so on. For example,
288 -- to catch just calls to the 'error' function, we could use
290 -- > result <- catchJust errorCalls thing_to_try handler
292 -- Any other exceptions which are not matched by the predicate
293 -- are re-raised, and may be caught by an enclosing
294 -- 'catch' or 'catchJust'.
296 :: (Exception -> Maybe b) -- ^ Predicate to select exceptions
297 -> IO a -- ^ Computation to run
298 -> (b -> IO a) -- ^ Handler
300 catchJust p a handler = catch a handler'
301 where handler' e = case p e of
305 -- | A version of 'catch' with the arguments swapped around; useful in
306 -- situations where the code for the handler is shorter. For example:
308 -- > do handle (\e -> exitWith (ExitFailure 1)) $
310 handle :: (Exception -> IO a) -> IO a -> IO a
313 -- | A version of 'catchJust' with the arguments swapped around (see
315 handleJust :: (Exception -> Maybe b) -> (b -> IO a) -> IO a -> IO a
316 handleJust p = flip (catchJust p)
318 -----------------------------------------------------------------------------
321 -- | This function maps one exception into another as proposed in the
322 -- paper \"A semantics for imprecise exceptions\".
324 -- Notice that the usage of 'unsafePerformIO' is safe here.
326 mapException :: (Exception -> Exception) -> a -> a
327 mapException f v = unsafePerformIO (catch (evaluate v)
330 -----------------------------------------------------------------------------
331 -- 'try' and variations.
333 -- | Similar to 'catch', but returns an 'Either' result which is
334 -- @('Right' a)@ if no exception was raised, or @('Left' e)@ if an
335 -- exception was raised and its value is @e@.
337 -- > try a = catch (Right `liftM` a) (return . Left)
339 -- Note: as with 'catch', it is only polite to use this variant if you intend
340 -- to re-throw the exception after performing whatever cleanup is needed.
341 -- Otherwise, 'tryJust' is generally considered to be better.
343 -- Also note that "System.IO.Error" also exports a function called
344 -- 'System.IO.Error.try' with a similar type to 'Control.OldException.try',
345 -- except that it catches only the IO and user families of exceptions
346 -- (as required by the Haskell 98 @IO@ module).
348 try :: IO a -> IO (Either Exception a)
349 try a = catch (a >>= \ v -> return (Right v)) (\e -> return (Left e))
351 -- | A variant of 'try' that takes an exception predicate to select
352 -- which exceptions are caught (c.f. 'catchJust'). If the exception
353 -- does not match the predicate, it is re-thrown.
354 tryJust :: (Exception -> Maybe b) -> IO a -> IO (Either b a)
358 Right v -> return (Right v)
359 Left e -> case p e of
361 Just b -> return (Left b)
363 -----------------------------------------------------------------------------
364 -- Dynamic exceptions
367 -- #DynamicExceptions# Because the 'Exception' datatype is not extensible, there is an
368 -- interface for throwing and catching exceptions of type 'Dynamic'
369 -- (see "Data.Dynamic") which allows exception values of any type in
370 -- the 'Typeable' class to be thrown and caught.
372 -- | Raise any value as an exception, provided it is in the
374 throwDyn :: Typeable exception => exception -> b
376 throwDyn exception = throw (UserError "" "dynamic exception")
378 throwDyn exception = throw (DynException (toDyn exception))
381 #ifdef __GLASGOW_HASKELL__
382 -- | A variant of 'throwDyn' that throws the dynamic exception to an
383 -- arbitrary thread (GHC only: c.f. 'throwTo').
384 throwDynTo :: Typeable exception => ThreadId -> exception -> IO ()
385 throwDynTo t exception = New.throwTo t (DynException (toDyn exception))
386 #endif /* __GLASGOW_HASKELL__ */
388 -- | Catch dynamic exceptions of the required type. All other
389 -- exceptions are re-thrown, including dynamic exceptions of the wrong
392 -- When using dynamic exceptions it is advisable to define a new
393 -- datatype to use for your exception type, to avoid possible clashes
394 -- with dynamic exceptions used in other libraries.
396 catchDyn :: Typeable exception => IO a -> (exception -> IO a) -> IO a
398 catchDyn m k = m -- can't catch dyn exceptions in nhc98
400 catchDyn m k = catchException m handle
401 where handle ex = case ex of
402 (DynException dyn) ->
403 case fromDynamic dyn of
404 Just exception -> k exception
409 -----------------------------------------------------------------------------
410 -- Exception Predicates
413 -- These pre-defined predicates may be used as the first argument to
414 -- 'catchJust', 'tryJust', or 'handleJust' to select certain common
415 -- classes of exceptions.
417 ioErrors :: Exception -> Maybe IOError
418 arithExceptions :: Exception -> Maybe New.ArithException
419 errorCalls :: Exception -> Maybe String
420 assertions :: Exception -> Maybe String
421 dynExceptions :: Exception -> Maybe Dynamic
422 asyncExceptions :: Exception -> Maybe New.AsyncException
423 userErrors :: Exception -> Maybe String
425 ioErrors (IOException e) = Just e
428 arithExceptions (ArithException e) = Just e
429 arithExceptions _ = Nothing
431 errorCalls (ErrorCall e) = Just e
432 errorCalls _ = Nothing
434 assertions (AssertionFailed e) = Just e
435 assertions _ = Nothing
437 dynExceptions (DynException e) = Just e
438 dynExceptions _ = Nothing
440 asyncExceptions (AsyncException e) = Just e
441 asyncExceptions _ = Nothing
443 userErrors (IOException e) | isUserError e = Just (ioeGetErrorString e)
444 userErrors _ = Nothing
446 -----------------------------------------------------------------------------
447 -- Some Useful Functions
449 -- | When you want to acquire a resource, do some work with it, and
450 -- then release the resource, it is a good idea to use 'bracket',
451 -- because 'bracket' will install the necessary exception handler to
452 -- release the resource in the event that an exception is raised
453 -- during the computation. If an exception is raised, then 'bracket' will
454 -- re-raise the exception (after performing the release).
456 -- A common example is opening a file:
459 -- > (openFile "filename" ReadMode)
461 -- > (\handle -> do { ... })
463 -- The arguments to 'bracket' are in this order so that we can partially apply
466 -- > withFile name mode = bracket (openFile name mode) hClose
470 :: IO a -- ^ computation to run first (\"acquire resource\")
471 -> (a -> IO b) -- ^ computation to run last (\"release resource\")
472 -> (a -> IO c) -- ^ computation to run in-between
473 -> IO c -- returns the value from the in-between computation
474 bracket before after thing =
479 (\e -> do { after a; throw e })
485 -- | A specialised variant of 'bracket' with just a computation to run
488 finally :: IO a -- ^ computation to run first
489 -> IO b -- ^ computation to run afterward (even if an exception
491 -> IO a -- returns the value from the first computation
496 (\e -> do { sequel; throw e })
501 -- | A variant of 'bracket' where the return value from the first computation
503 bracket_ :: IO a -> IO b -> IO c -> IO c
504 bracket_ before after thing = bracket before (const after) (const thing)
506 -- | Like bracket, but only performs the final action if there was an
507 -- exception raised by the in-between computation.
509 :: IO a -- ^ computation to run first (\"acquire resource\")
510 -> (a -> IO b) -- ^ computation to run last (\"release resource\")
511 -> (a -> IO c) -- ^ computation to run in-between
512 -> IO c -- returns the value from the in-between computation
513 bracketOnError before after thing =
518 (\e -> do { after a; throw e })
521 -- -----------------------------------------------------------------------------
522 -- Asynchronous exceptions
526 #AsynchronousExceptions# Asynchronous exceptions are so-called because they arise due to
527 external influences, and can be raised at any point during execution.
528 'StackOverflow' and 'HeapOverflow' are two examples of
529 system-generated asynchronous exceptions.
531 The primary source of asynchronous exceptions, however, is
534 > throwTo :: ThreadId -> Exception -> IO ()
536 'throwTo' (also 'throwDynTo' and 'Control.Concurrent.killThread') allows one
537 running thread to raise an arbitrary exception in another thread. The
538 exception is therefore asynchronous with respect to the target thread,
539 which could be doing anything at the time it receives the exception.
540 Great care should be taken with asynchronous exceptions; it is all too
541 easy to introduce race conditions by the over zealous use of
546 There\'s an implied 'block' around every exception handler in a call
547 to one of the 'catch' family of functions. This is because that is
548 what you want most of the time - it eliminates a common race condition
549 in starting an exception handler, because there may be no exception
550 handler on the stack to handle another exception if one arrives
551 immediately. If asynchronous exceptions are blocked on entering the
552 handler, though, we have time to install a new exception handler
553 before being interrupted. If this weren\'t the default, one would have
554 to write something like
557 > catch (unblock (...))
561 If you need to unblock asynchronous exceptions again in the exception
562 handler, just use 'unblock' as normal.
564 Note that 'try' and friends /do not/ have a similar default, because
565 there is no exception handler in this case. If you want to use 'try'
566 in an asynchronous-exception-safe way, you will need to use
572 Some operations are /interruptible/, which means that they can receive
573 asynchronous exceptions even in the scope of a 'block'. Any function
574 which may itself block is defined as interruptible; this includes
575 'Control.Concurrent.MVar.takeMVar'
576 (but not 'Control.Concurrent.MVar.tryTakeMVar'),
577 and most operations which perform
578 some I\/O with the outside world. The reason for having
579 interruptible operations is so that we can write things like
583 > catch (unblock (...))
587 if the 'Control.Concurrent.MVar.takeMVar' was not interruptible,
589 combination could lead to deadlock, because the thread itself would be
590 blocked in a state where it can\'t receive any asynchronous exceptions.
591 With 'Control.Concurrent.MVar.takeMVar' interruptible, however, we can be
592 safe in the knowledge that the thread can receive exceptions right up
593 until the point when the 'Control.Concurrent.MVar.takeMVar' succeeds.
594 Similar arguments apply for other interruptible operations like
595 'System.IO.openFile'.
598 #if !(__GLASGOW_HASKELL__ || __NHC__)
599 assert :: Bool -> a -> a
601 assert False _ = throw (AssertionFailed "")
605 #ifdef __GLASGOW_HASKELL__
606 {-# NOINLINE uncaughtExceptionHandler #-}
607 uncaughtExceptionHandler :: IORef (Exception -> IO ())
608 uncaughtExceptionHandler = unsafePerformIO (newIORef defaultHandler)
610 defaultHandler :: Exception -> IO ()
611 defaultHandler ex = do
612 (hFlush stdout) `New.catchAny` (\ _ -> return ())
614 Deadlock -> "no threads to run: infinite loop or deadlock?"
616 other -> showsPrec 0 other ""
617 withCString "%s" $ \cfmt ->
618 withCString msg $ \cmsg ->
621 -- don't use errorBelch() directly, because we cannot call varargs functions
623 foreign import ccall unsafe "HsBase.h errorBelch2"
624 errorBelch :: CString -> CString -> IO ()
626 setUncaughtExceptionHandler :: (Exception -> IO ()) -> IO ()
627 setUncaughtExceptionHandler = writeIORef uncaughtExceptionHandler
629 getUncaughtExceptionHandler :: IO (Exception -> IO ())
630 getUncaughtExceptionHandler = readIORef uncaughtExceptionHandler
633 -- ------------------------------------------------------------------------
634 -- Exception datatype and operations
636 -- |The type of exceptions. Every kind of system-generated exception
637 -- has a constructor in the 'Exception' type, and values of other
638 -- types may be injected into 'Exception' by coercing them to
639 -- 'Data.Dynamic.Dynamic' (see the section on Dynamic Exceptions:
640 -- "Control.OldException\#DynamicExceptions").
642 = ArithException New.ArithException
643 -- ^Exceptions raised by arithmetic
644 -- operations. (NOTE: GHC currently does not throw
645 -- 'ArithException's except for 'DivideByZero').
646 | ArrayException New.ArrayException
647 -- ^Exceptions raised by array-related
648 -- operations. (NOTE: GHC currently does not throw
649 -- 'ArrayException's).
650 | AssertionFailed String
651 -- ^This exception is thrown by the
652 -- 'assert' operation when the condition
653 -- fails. The 'String' argument contains the
654 -- location of the assertion in the source program.
655 | AsyncException New.AsyncException
656 -- ^Asynchronous exceptions (see section on Asynchronous Exceptions: "Control.OldException\#AsynchronousExceptions").
658 -- ^The current thread was executing a call to
659 -- 'Control.Concurrent.MVar.takeMVar' that could never return,
660 -- because there are no other references to this 'MVar'.
661 | BlockedIndefinitely
662 -- ^The current thread was waiting to retry an atomic memory transaction
663 -- that could never become possible to complete because there are no other
664 -- threads referring to any of the TVars involved.
666 -- ^The runtime detected an attempt to nest one STM transaction
667 -- inside another one, presumably due to the use of
668 -- 'unsafePeformIO' with 'atomically'.
670 -- ^There are no runnable threads, so the program is
671 -- deadlocked. The 'Deadlock' exception is
672 -- raised in the main thread only (see also: "Control.Concurrent").
673 | DynException Dynamic
674 -- ^Dynamically typed exceptions (see section on Dynamic Exceptions: "Control.OldException\#DynamicExceptions").
676 -- ^The 'ErrorCall' exception is thrown by 'error'. The 'String'
677 -- argument of 'ErrorCall' is the string passed to 'error' when it was
679 | ExitException New.ExitCode
680 -- ^The 'ExitException' exception is thrown by 'System.Exit.exitWith' (and
681 -- 'System.Exit.exitFailure'). The 'ExitCode' argument is the value passed
682 -- to 'System.Exit.exitWith'. An unhandled 'ExitException' exception in the
683 -- main thread will cause the program to be terminated with the given
685 | IOException New.IOException
686 -- ^These are the standard IO exceptions generated by
687 -- Haskell\'s @IO@ operations. See also "System.IO.Error".
688 | NoMethodError String
689 -- ^An attempt was made to invoke a class method which has
690 -- no definition in this instance, and there was no default
691 -- definition given in the class declaration. GHC issues a
692 -- warning when you compile an instance which has missing
695 -- ^The current thread is stuck in an infinite loop. This
696 -- exception may or may not be thrown when the program is
698 | PatternMatchFail String
699 -- ^A pattern matching failure. The 'String' argument should contain a
700 -- descriptive message including the function name, source file
703 -- ^An attempt was made to evaluate a field of a record
704 -- for which no value was given at construction time. The
705 -- 'String' argument gives the location of the
706 -- record construction in the source program.
708 -- ^A field selection was attempted on a constructor that
709 -- doesn\'t have the requested field. This can happen with
710 -- multi-constructor records when one or more fields are
711 -- missing from some of the constructors. The
712 -- 'String' argument gives the location of the
713 -- record selection in the source program.
715 -- ^An attempt was made to update a field in a record,
716 -- where the record doesn\'t have the requested field. This can
717 -- only occur with multi-constructor records, when one or more
718 -- fields are missing from some of the constructors. The
719 -- 'String' argument gives the location of the
720 -- record update in the source program.
721 INSTANCE_TYPEABLE0(Exception,exceptionTc,"Exception")
723 nonTermination :: SomeException
724 nonTermination = New.toException NonTermination
726 -- For now at least, make the monolithic Exception type an instance of
727 -- the Exception class
728 instance ExceptionBase.Exception Exception
730 instance Show Exception where
731 showsPrec _ (IOException err) = shows err
732 showsPrec _ (ArithException err) = shows err
733 showsPrec _ (ArrayException err) = shows err
734 showsPrec _ (ErrorCall err) = showString err
735 showsPrec _ (ExitException err) = showString "exit: " . shows err
736 showsPrec _ (NoMethodError err) = showString err
737 showsPrec _ (PatternMatchFail err) = showString err
738 showsPrec _ (RecSelError err) = showString err
739 showsPrec _ (RecConError err) = showString err
740 showsPrec _ (RecUpdError err) = showString err
741 showsPrec _ (AssertionFailed err) = showString err
742 showsPrec _ (DynException err) = showString "exception :: " . showsTypeRep (dynTypeRep err)
743 showsPrec _ (AsyncException e) = shows e
744 showsPrec p BlockedOnDeadMVar = showsPrec p New.BlockedOnDeadMVar
745 showsPrec p BlockedIndefinitely = showsPrec p New.BlockedIndefinitely
746 showsPrec p NestedAtomically = showsPrec p New.NestedAtomically
747 showsPrec p NonTermination = showsPrec p New.NonTermination
748 showsPrec p Deadlock = showsPrec p New.Deadlock
750 instance Eq Exception where
751 IOException e1 == IOException e2 = e1 == e2
752 ArithException e1 == ArithException e2 = e1 == e2
753 ArrayException e1 == ArrayException e2 = e1 == e2
754 ErrorCall e1 == ErrorCall e2 = e1 == e2
755 ExitException e1 == ExitException e2 = e1 == e2
756 NoMethodError e1 == NoMethodError e2 = e1 == e2
757 PatternMatchFail e1 == PatternMatchFail e2 = e1 == e2
758 RecSelError e1 == RecSelError e2 = e1 == e2
759 RecConError e1 == RecConError e2 = e1 == e2
760 RecUpdError e1 == RecUpdError e2 = e1 == e2
761 AssertionFailed e1 == AssertionFailed e2 = e1 == e2
762 DynException _ == DynException _ = False -- incomparable
763 AsyncException e1 == AsyncException e2 = e1 == e2
764 BlockedOnDeadMVar == BlockedOnDeadMVar = True
765 NonTermination == NonTermination = True
766 NestedAtomically == NestedAtomically = True
767 Deadlock == Deadlock = True