+{-# OPTIONS_GHC -XNoImplicitPrelude #-}
+
+#include "Typeable.h"
+
-----------------------------------------------------------------------------
-- |
-- Module : Control.Exception
-- Copyright : (c) The University of Glasgow 2001
--- License : BSD-style (see the file libraries/core/LICENSE)
+-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
--- Portability : non-portable
+-- Portability : non-portable (extended exceptions)
+--
+-- This module provides support for raising and catching both built-in
+-- and user-defined exceptions.
+--
+-- In addition to exceptions thrown by 'IO' operations, exceptions may
+-- be thrown by pure code (imprecise exceptions) or by external events
+-- (asynchronous exceptions), but may only be caught in the 'IO' monad.
+-- For more details, see:
+--
+-- * /A semantics for imprecise exceptions/, by Simon Peyton Jones,
+-- Alastair Reid, Tony Hoare, Simon Marlow, Fergus Henderson,
+-- in /PLDI'99/.
--
--- The External API for exceptions. The functions provided in this
--- module allow catching of exceptions in the IO monad.
+-- * /Asynchronous exceptions in Haskell/, by Simon Marlow, Simon Peyton
+-- Jones, Andy Moran and John Reppy, in /PLDI'01/.
--
-----------------------------------------------------------------------------
module Control.Exception (
- Exception(..), -- instance Eq, Ord, Show, Typeable
- IOException, -- instance Eq, Ord, Show, Typeable
- ArithException(..), -- instance Eq, Ord, Show, Typeable
- ArrayException(..), -- instance Eq, Ord, Show, Typeable
- AsyncException(..), -- instance Eq, Ord, Show, Typeable
+ -- * The Exception type
+ SomeException(..),
+ Exception(..), -- instance Eq, Ord, Show, Typeable
+ IOException, -- instance Eq, Ord, Show, Typeable
+ ArithException(..), -- instance Eq, Ord, Show, Typeable
+ ArrayException(..), -- instance Eq, Ord, Show, Typeable
+ AssertionFailed(..),
+ AsyncException(..), -- instance Eq, Ord, Show, Typeable
+ NonTermination(..), nonTermination,
+ BlockedOnDeadMVar(..),
+ BlockedIndefinitely(..),
+ NestedAtomically(..), nestedAtomically,
+ Deadlock(..),
+ NoMethodError(..),
+ PatternMatchFail(..),
+ RecConError(..),
+ RecSelError(..),
+ RecUpdError(..),
+ ErrorCall(..),
+
+ -- * Throwing exceptions
+ throwIO, -- :: Exception -> IO a
+ throw, -- :: Exception -> a
+ ioError, -- :: IOError -> IO a
+#ifdef __GLASGOW_HASKELL__
+ throwTo, -- :: ThreadId -> Exception -> a
+#endif
- try, -- :: IO a -> IO (Either Exception a)
- tryJust, -- :: (Exception -> Maybe b) -> a -> IO (Either b a)
+ -- * Catching Exceptions
- catch, -- :: IO a -> (Exception -> IO a) -> IO a
- catchJust, -- :: (Exception -> Maybe b) -> IO a -> (b -> IO a) -> IO a
+ -- |There are several functions for catching and examining
+ -- exceptions; all of them may only be used from within the
+ -- 'IO' monad.
- handle, -- :: (Exception -> IO a) -> IO a -> IO a
- handleJust,-- :: (Exception -> Maybe b) -> (b -> IO a) -> IO a -> IO a
+ -- ** The @catch@ functions
+ catch, -- :: IO a -> (Exception -> IO a) -> IO a
+ catches, Handler(..),
+ catchAny,
+ catchJust, -- :: (Exception -> Maybe b) -> IO a -> (b -> IO a) -> IO a
- evaluate, -- :: a -> IO a
+ -- ** The @handle@ functions
+ handle, -- :: (Exception -> IO a) -> IO a -> IO a
+ handleAny,
+ handleJust,-- :: (Exception -> Maybe b) -> (b -> IO a) -> IO a -> IO a
- -- Exception predicates (for tryJust, catchJust, handleJust)
+ -- ** The @try@ functions
+ try, -- :: IO a -> IO (Either Exception a)
+ tryJust, -- :: (Exception -> Maybe b) -> a -> IO (Either b a)
+ ignoreExceptions,
+ onException,
- ioErrors, -- :: Exception -> Maybe IOError
- arithExceptions, -- :: Exception -> Maybe ArithException
- errorCalls, -- :: Exception -> Maybe String
- dynExceptions, -- :: Exception -> Maybe Dynamic
- assertions, -- :: Exception -> Maybe String
- asyncExceptions, -- :: Exception -> Maybe AsyncException
- userErrors, -- :: Exception -> Maybe String
+ -- ** The @evaluate@ function
+ evaluate, -- :: a -> IO a
- -- Throwing exceptions
+ -- ** The @mapException@ function
+ mapException, -- :: (Exception -> Exception) -> a -> a
- throw, -- :: Exception -> a
- throwTo, -- :: ThreadId -> Exception -> a
+ -- * Asynchronous Exceptions
- -- Dynamic exceptions
+ -- $async
- throwDyn, -- :: Typeable ex => ex -> b
- throwDynTo, -- :: Typeable ex => ThreadId -> ex -> b
- catchDyn, -- :: Typeable ex => IO a -> (ex -> IO a) -> IO a
-
- -- Async exception control
+ -- ** Asynchronous exception control
+
+ -- |The following two functions allow a thread to control delivery of
+ -- asynchronous exceptions during a critical region.
block, -- :: IO a -> IO a
unblock, -- :: IO a -> IO a
+ blocked, -- :: IO Bool
+
+ -- *** Applying @block@ to an exception handler
- -- Assertions
+ -- $block_handler
- -- for now
- assert, -- :: Bool -> a -> a
+ -- *** Interruptible operations
- -- Utilities
+ -- $interruptible
- finally, -- :: IO a -> IO b -> IO b
+ -- * Assertions
- bracket, -- :: IO a -> (a -> IO b) -> (a -> IO c) -> IO ()
- bracket_, -- :: IO a -> IO b -> IO c -> IO ()
+ assert, -- :: Bool -> a -> a
+ -- * Utilities
+
+ bracket, -- :: IO a -> (a -> IO b) -> (a -> IO c) -> IO ()
+ bracket_, -- :: IO a -> IO b -> IO c -> IO ()
+ bracketOnError,
+
+ finally, -- :: IO a -> IO b -> IO a
+
+ recSelError, recConError, irrefutPatError, runtimeError,
+ nonExhaustiveGuardsError, patError, noMethodBindingError,
+
+#ifdef __GLASGOW_HASKELL__
+ setUncaughtExceptionHandler, -- :: (Exception -> IO ()) -> IO ()
+ getUncaughtExceptionHandler -- :: IO (Exception -> IO ())
+#endif
) where
#ifdef __GLASGOW_HASKELL__
-import Prelude hiding (catch)
-import System.IO.Error
-import GHC.Base ( assert )
-import GHC.Exception hiding (try, catch, bracket, bracket_)
-import GHC.Conc ( throwTo, ThreadId )
-import GHC.IOBase ( IO(..) )
+import GHC.Base
+import GHC.IOBase
+import {-# SOURCE #-} GHC.Handle
+import GHC.List
+import GHC.Num
+import GHC.Show
+import GHC.IOBase as ExceptionBase
+import GHC.Exception hiding ( Exception )
+import {-# SOURCE #-} GHC.Conc ( ThreadId(ThreadId) )
+import Foreign.C.String ( CString, withCString )
#endif
#ifdef __HUGS__
-import Prelude hiding ( catch )
-import PrelPrim ( catchException
- , Exception(..)
- , throw
- , ArithException(..)
- , AsyncException(..)
- , assert
- )
+import Hugs.Exception as ExceptionBase
#endif
import Data.Dynamic
+import Data.Either
+import Data.Maybe
+
+#ifdef __NHC__
+import qualified System.IO.Error as H'98 (catch)
+import System.IO.Error (ioError)
+import IO (bracket)
+import DIOError -- defn of IOError type
+import System (ExitCode())
+
+-- minimum needed for nhc98 to pretend it has Exceptions
+data Exception = IOException IOException
+ | ArithException ArithException
+ | ArrayException ArrayException
+ | AsyncException AsyncException
+ | ExitException ExitCode
+ deriving Show
+type IOException = IOError
+data ArithException
+data ArrayException
+data AsyncException
+instance Show ArithException
+instance Show ArrayException
+instance Show AsyncException
+
+catch :: IO a -> (Exception -> IO a) -> IO a
+a `catch` b = a `H'98.catch` (b . IOException)
+
+throwIO :: Exception -> IO a
+throwIO (IOException e) = ioError e
+throwIO _ = ioError (UserError "Control.Exception.throwIO"
+ "unknown exception")
+throw :: Exception -> a
+throw = unsafePerformIO . throwIO
-#include "Dynamic.h"
-INSTANCE_TYPEABLE0(Exception,exceptionTc,"Exception")
-INSTANCE_TYPEABLE0(IOException,ioExceptionTc,"IOException")
-INSTANCE_TYPEABLE0(ArithException,arithExceptionTc,"ArithException")
-INSTANCE_TYPEABLE0(ArrayException,arrayExceptionTc,"ArrayException")
-INSTANCE_TYPEABLE0(AsyncException,asyncExceptionTc,"AsyncException")
+evaluate :: a -> IO a
+evaluate x = x `seq` return x
------------------------------------------------------------------------------
--- Catching exceptions
+assert :: Bool -> a -> a
+assert True x = x
+assert False _ = throw (IOException (UserError "" "Assertion failed"))
+#endif
--- GHC.Exception defines 'catchException' for us.
+#ifndef __GLASGOW_HASKELL__
+-- Dummy definitions for implementations lacking asynchonous exceptions
+
+block :: IO a -> IO a
+block = id
+unblock :: IO a -> IO a
+unblock = id
+blocked :: IO Bool
+blocked = return False
+#endif
-catch :: IO a -> (Exception -> IO a) -> IO a
-catch = catchException
+-----------------------------------------------------------------------------
+-- Catching exceptions
-catchJust :: (Exception -> Maybe b) -> IO a -> (b -> IO a) -> IO a
+-- |This is the simplest of the exception-catching functions. It
+-- takes a single argument, runs it, and if an exception is raised
+-- the \"handler\" is executed, with the value of the exception passed as an
+-- argument. Otherwise, the result is returned as normal. For example:
+--
+-- > catch (openFile f ReadMode)
+-- > (\e -> hPutStr stderr ("Couldn't open "++f++": " ++ show e))
+--
+-- For catching exceptions in pure (non-'IO') expressions, see the
+-- function 'evaluate'.
+--
+-- Note that due to Haskell\'s unspecified evaluation order, an
+-- expression may return one of several possible exceptions: consider
+-- the expression @error \"urk\" + 1 \`div\` 0@. Does
+-- 'catch' execute the handler passing
+-- @ErrorCall \"urk\"@, or @ArithError DivideByZero@?
+--
+-- The answer is \"either\": 'catch' makes a
+-- non-deterministic choice about which exception to catch. If you
+-- call it again, you might get a different exception back. This is
+-- ok, because 'catch' is an 'IO' computation.
+--
+-- Note that 'catch' catches all types of exceptions, and is generally
+-- used for \"cleaning up\" before passing on the exception using
+-- 'throwIO'. It is not good practice to discard the exception and
+-- continue, without first checking the type of the exception (it
+-- might be a 'ThreadKilled', for example). In this case it is usually better
+-- to use 'catchJust' and select the kinds of exceptions to catch.
+--
+-- Also note that the "Prelude" also exports a function called
+-- 'Prelude.catch' with a similar type to 'Control.Exception.catch',
+-- except that the "Prelude" version only catches the IO and user
+-- families of exceptions (as required by Haskell 98).
+--
+-- We recommend either hiding the "Prelude" version of 'Prelude.catch'
+-- when importing "Control.Exception":
+--
+-- > import Prelude hiding (catch)
+--
+-- or importing "Control.Exception" qualified, to avoid name-clashes:
+--
+-- > import qualified Control.Exception as C
+--
+-- and then using @C.catch@
+--
+#ifndef __NHC__
+catch :: Exception e
+ => IO a -- ^ The computation to run
+ -> (e -> IO a) -- ^ Handler to invoke if an exception is raised
+ -> IO a
+catch = ExceptionBase.catchException
+
+catches :: IO a -> [Handler a] -> IO a
+catches io handlers = io `catch` catchesHandler handlers
+
+catchesHandler :: [Handler a] -> SomeException -> IO a
+catchesHandler handlers e = foldr tryHandler (throw e) handlers
+ where tryHandler (Handler handler) res
+ = case fromException e of
+ Just e' -> handler e'
+ Nothing -> res
+
+data Handler a = forall e . Exception e => Handler (e -> IO a)
+#endif
+-- | The function 'catchJust' is like 'catch', but it takes an extra
+-- argument which is an /exception predicate/, a function which
+-- selects which type of exceptions we\'re interested in.
+--
+-- > result <- catchJust errorCalls thing_to_try handler
+--
+-- Any other exceptions which are not matched by the predicate
+-- are re-raised, and may be caught by an enclosing
+-- 'catch' or 'catchJust'.
+catchJust
+ :: Exception e
+ => (e -> Maybe b) -- ^ Predicate to select exceptions
+ -> IO a -- ^ Computation to run
+ -> (b -> IO a) -- ^ Handler
+ -> IO a
catchJust p a handler = catch a handler'
where handler' e = case p e of
- Nothing -> throw e
- Just b -> handler b
+ Nothing -> throw e
+ Just b -> handler b
-handle :: (Exception -> IO a) -> IO a -> IO a
+-- | A version of 'catch' with the arguments swapped around; useful in
+-- situations where the code for the handler is shorter. For example:
+--
+-- > do handle (\e -> exitWith (ExitFailure 1)) $
+-- > ...
+handle :: Exception e => (e -> IO a) -> IO a -> IO a
handle = flip catch
-handleJust :: (Exception -> Maybe b) -> (b -> IO a) -> IO a -> IO a
+handleAny :: (forall e . Exception e => e -> IO a) -> IO a -> IO a
+handleAny = flip catchAny
+
+-- | A version of 'catchJust' with the arguments swapped around (see
+-- 'handle').
+handleJust :: Exception e => (e -> Maybe b) -> (b -> IO a) -> IO a -> IO a
handleJust p = flip (catchJust p)
-----------------------------------------------------------------------------
--- evaluate
+-- 'mapException'
-evaluate :: a -> IO a
-evaluate a = a `seq` return a
+-- | This function maps one exception into another as proposed in the
+-- paper \"A semantics for imprecise exceptions\".
+
+-- Notice that the usage of 'unsafePerformIO' is safe here.
+
+mapException :: Exception e => (e -> e) -> a -> a
+mapException f v = unsafePerformIO (catch (evaluate v)
+ (\x -> throw (f x)))
-----------------------------------------------------------------------------
-- 'try' and variations.
-try :: IO a -> IO (Either Exception a)
+-- | Similar to 'catch', but returns an 'Either' result which is
+-- @('Right' a)@ if no exception was raised, or @('Left' e)@ if an
+-- exception was raised and its value is @e@.
+--
+-- > try a = catch (Right `liftM` a) (return . Left)
+--
+-- Note: as with 'catch', it is only polite to use this variant if you intend
+-- to re-throw the exception after performing whatever cleanup is needed.
+-- Otherwise, 'tryJust' is generally considered to be better.
+--
+-- Also note that "System.IO.Error" also exports a function called
+-- 'System.IO.Error.try' with a similar type to 'Control.Exception.try',
+-- except that it catches only the IO and user families of exceptions
+-- (as required by the Haskell 98 @IO@ module).
+
+try :: Exception e => IO a -> IO (Either e a)
try a = catch (a >>= \ v -> return (Right v)) (\e -> return (Left e))
-tryJust :: (Exception -> Maybe b) -> IO a -> IO (Either b a)
+-- | A variant of 'try' that takes an exception predicate to select
+-- which exceptions are caught (c.f. 'catchJust'). If the exception
+-- does not match the predicate, it is re-thrown.
+tryJust :: Exception e => (e -> Maybe b) -> IO a -> IO (Either b a)
tryJust p a = do
r <- try a
case r of
- Right v -> return (Right v)
- Left e -> case p e of
- Nothing -> throw e
- Just b -> return (Left b)
-
------------------------------------------------------------------------------
--- Dynamic exception types. Since one of the possible kinds of exception
--- is a dynamically typed value, we can effectively have polymorphic
--- exceptions.
+ Right v -> return (Right v)
+ Left e -> case p e of
+ Nothing -> throw e
+ Just b -> return (Left b)
--- throwDyn will raise any value as an exception, provided it is in the
--- Typeable class (see Dynamic.lhs).
+ignoreExceptions :: IO () -> IO ()
+ignoreExceptions io = io `catchAny` \_ -> return ()
--- catchDyn will catch any exception of a given type (determined by the
--- handler function). Any raised exceptions that don't match are
--- re-raised.
-
-throwDyn :: Typeable exception => exception -> b
-throwDyn exception = throw (DynException (toDyn exception))
-
-throwDynTo :: Typeable exception => ThreadId -> exception -> IO ()
-throwDynTo t exception = throwTo t (DynException (toDyn exception))
-
-catchDyn :: Typeable exception => IO a -> (exception -> IO a) -> IO a
-catchDyn m k = catchException m handle
- where handle ex = case ex of
- (DynException dyn) ->
- case fromDynamic dyn of
- Just exception -> k exception
- Nothing -> throw ex
- _ -> throw ex
-
------------------------------------------------------------------------------
--- Exception Predicates
-
-ioErrors :: Exception -> Maybe IOError
-arithExceptions :: Exception -> Maybe ArithException
-errorCalls :: Exception -> Maybe String
-dynExceptions :: Exception -> Maybe Dynamic
-assertions :: Exception -> Maybe String
-asyncExceptions :: Exception -> Maybe AsyncException
-userErrors :: Exception -> Maybe String
-
-ioErrors e@(IOException _) = Just e
-ioErrors _ = Nothing
-
-arithExceptions (ArithException e) = Just e
-arithExceptions _ = Nothing
-
-errorCalls (ErrorCall e) = Just e
-errorCalls _ = Nothing
-
-assertions (AssertionFailed e) = Just e
-assertions _ = Nothing
-
-dynExceptions (DynException e) = Just e
-dynExceptions _ = Nothing
-
-asyncExceptions (AsyncException e) = Just e
-asyncExceptions _ = Nothing
-
-userErrors e | isUserError e = Just (ioeGetErrorString e)
-userErrors _ = Nothing
+onException :: IO a -> IO () -> IO a
+onException io what = io `catch` \e -> do what
+ throw (e :: SomeException)
-----------------------------------------------------------------------------
-- Some Useful Functions
-bracket :: IO a -> (a -> IO b) -> (a -> IO c) -> IO c
+-- | When you want to acquire a resource, do some work with it, and
+-- then release the resource, it is a good idea to use 'bracket',
+-- because 'bracket' will install the necessary exception handler to
+-- release the resource in the event that an exception is raised
+-- during the computation. If an exception is raised, then 'bracket' will
+-- re-raise the exception (after performing the release).
+--
+-- A common example is opening a file:
+--
+-- > bracket
+-- > (openFile "filename" ReadMode)
+-- > (hClose)
+-- > (\handle -> do { ... })
+--
+-- The arguments to 'bracket' are in this order so that we can partially apply
+-- it, e.g.:
+--
+-- > withFile name mode = bracket (openFile name mode) hClose
+--
+#ifndef __NHC__
+bracket
+ :: IO a -- ^ computation to run first (\"acquire resource\")
+ -> (a -> IO b) -- ^ computation to run last (\"release resource\")
+ -> (a -> IO c) -- ^ computation to run in-between
+ -> IO c -- returns the value from the in-between computation
bracket before after thing =
block (do
a <- before
- r <- catch
- (unblock (thing a))
- (\e -> do { after a; throw e })
+ r <- catchAny
+ (unblock (thing a))
+ (\e -> do { after a; throw e })
after a
return r
)
-
--- finally is an instance of bracket, but it's quite common
--- so we give the specialised version for efficiency.
-finally :: IO a -> IO b -> IO a
+#endif
+
+-- | A specialised variant of 'bracket' with just a computation to run
+-- afterward.
+--
+finally :: IO a -- ^ computation to run first
+ -> IO b -- ^ computation to run afterward (even if an exception
+ -- was raised)
+ -> IO a -- returns the value from the first computation
a `finally` sequel =
block (do
- r <- catch
- (unblock a)
- (\e -> do { sequel; throw e })
+ r <- catchAny
+ (unblock a)
+ (\e -> do { sequel; throw e })
sequel
return r
)
+-- | A variant of 'bracket' where the return value from the first computation
+-- is not required.
bracket_ :: IO a -> IO b -> IO c -> IO c
bracket_ before after thing = bracket before (const after) (const thing)
+
+-- | Like bracket, but only performs the final action if there was an
+-- exception raised by the in-between computation.
+bracketOnError
+ :: IO a -- ^ computation to run first (\"acquire resource\")
+ -> (a -> IO b) -- ^ computation to run last (\"release resource\")
+ -> (a -> IO c) -- ^ computation to run in-between
+ -> IO c -- returns the value from the in-between computation
+bracketOnError before after thing =
+ block (do
+ a <- before
+ catchAny
+ (unblock (thing a))
+ (\e -> do { after a; throw e })
+ )
+
+-- -----------------------------------------------------------------------------
+-- Asynchronous exceptions
+
+{- $async
+
+ #AsynchronousExceptions# Asynchronous exceptions are so-called because they arise due to
+external influences, and can be raised at any point during execution.
+'StackOverflow' and 'HeapOverflow' are two examples of
+system-generated asynchronous exceptions.
+
+The primary source of asynchronous exceptions, however, is
+'throwTo':
+
+> throwTo :: ThreadId -> Exception -> IO ()
+
+'throwTo' (also 'throwDynTo' and 'Control.Concurrent.killThread') allows one
+running thread to raise an arbitrary exception in another thread. The
+exception is therefore asynchronous with respect to the target thread,
+which could be doing anything at the time it receives the exception.
+Great care should be taken with asynchronous exceptions; it is all too
+easy to introduce race conditions by the over zealous use of
+'throwTo'.
+-}
+
+{- $block_handler
+There\'s an implied 'block' around every exception handler in a call
+to one of the 'catch' family of functions. This is because that is
+what you want most of the time - it eliminates a common race condition
+in starting an exception handler, because there may be no exception
+handler on the stack to handle another exception if one arrives
+immediately. If asynchronous exceptions are blocked on entering the
+handler, though, we have time to install a new exception handler
+before being interrupted. If this weren\'t the default, one would have
+to write something like
+
+> block (
+> catch (unblock (...))
+> (\e -> handler)
+> )
+
+If you need to unblock asynchronous exceptions again in the exception
+handler, just use 'unblock' as normal.
+
+Note that 'try' and friends /do not/ have a similar default, because
+there is no exception handler in this case. If you want to use 'try'
+in an asynchronous-exception-safe way, you will need to use
+'block'.
+-}
+
+{- $interruptible
+
+Some operations are /interruptible/, which means that they can receive
+asynchronous exceptions even in the scope of a 'block'. Any function
+which may itself block is defined as interruptible; this includes
+'Control.Concurrent.MVar.takeMVar'
+(but not 'Control.Concurrent.MVar.tryTakeMVar'),
+and most operations which perform
+some I\/O with the outside world. The reason for having
+interruptible operations is so that we can write things like
+
+> block (
+> a <- takeMVar m
+> catch (unblock (...))
+> (\e -> ...)
+> )
+
+if the 'Control.Concurrent.MVar.takeMVar' was not interruptible,
+then this particular
+combination could lead to deadlock, because the thread itself would be
+blocked in a state where it can\'t receive any asynchronous exceptions.
+With 'Control.Concurrent.MVar.takeMVar' interruptible, however, we can be
+safe in the knowledge that the thread can receive exceptions right up
+until the point when the 'Control.Concurrent.MVar.takeMVar' succeeds.
+Similar arguments apply for other interruptible operations like
+'System.IO.openFile'.
+-}
+
+#if !(__GLASGOW_HASKELL__ || __NHC__)
+assert :: Bool -> a -> a
+assert True x = x
+assert False _ = throw (AssertionFailed "")
+#endif
+
+
+#ifdef __GLASGOW_HASKELL__
+{-# NOINLINE uncaughtExceptionHandler #-}
+uncaughtExceptionHandler :: IORef (SomeException -> IO ())
+uncaughtExceptionHandler = unsafePerformIO (newIORef defaultHandler)
+ where
+ defaultHandler :: SomeException -> IO ()
+ defaultHandler se@(SomeException ex) = do
+ (hFlush stdout) `catchAny` (\ _ -> return ())
+ let msg = case cast ex of
+ Just Deadlock -> "no threads to run: infinite loop or deadlock?"
+ _ -> case cast ex of
+ Just (ErrorCall s) -> s
+ _ -> showsPrec 0 se ""
+ withCString "%s" $ \cfmt ->
+ withCString msg $ \cmsg ->
+ errorBelch cfmt cmsg
+
+-- don't use errorBelch() directly, because we cannot call varargs functions
+-- using the FFI.
+foreign import ccall unsafe "HsBase.h errorBelch2"
+ errorBelch :: CString -> CString -> IO ()
+
+setUncaughtExceptionHandler :: (SomeException -> IO ()) -> IO ()
+setUncaughtExceptionHandler = writeIORef uncaughtExceptionHandler
+
+getUncaughtExceptionHandler :: IO (SomeException -> IO ())
+getUncaughtExceptionHandler = readIORef uncaughtExceptionHandler
+#endif
+
+recSelError, recConError, irrefutPatError, runtimeError,
+ nonExhaustiveGuardsError, patError, noMethodBindingError
+ :: Addr# -> a -- All take a UTF8-encoded C string
+
+recSelError s = throw (RecSelError (unpackCStringUtf8# s)) -- No location info unfortunately
+runtimeError s = error (unpackCStringUtf8# s) -- No location info unfortunately
+
+nonExhaustiveGuardsError s = throw (PatternMatchFail (untangle s "Non-exhaustive guards in"))
+irrefutPatError s = throw (PatternMatchFail (untangle s "Irrefutable pattern failed for pattern"))
+recConError s = throw (RecConError (untangle s "Missing field in record construction"))
+noMethodBindingError s = throw (NoMethodError (untangle s "No instance nor default method for class operation"))
+patError s = throw (PatternMatchFail (untangle s "Non-exhaustive patterns in"))
+
+-----
+
+data PatternMatchFail = PatternMatchFail String
+INSTANCE_TYPEABLE0(PatternMatchFail,patternMatchFailTc,"PatternMatchFail")
+
+instance Exception PatternMatchFail
+
+instance Show PatternMatchFail where
+ showsPrec _ (PatternMatchFail err) = showString err
+
+-----
+
+data RecSelError = RecSelError String
+INSTANCE_TYPEABLE0(RecSelError,recSelErrorTc,"RecSelError")
+
+instance Exception RecSelError
+
+instance Show RecSelError where
+ showsPrec _ (RecSelError err) = showString err
+
+-----
+
+data RecConError = RecConError String
+INSTANCE_TYPEABLE0(RecConError,recConErrorTc,"RecConError")
+
+instance Exception RecConError
+
+instance Show RecConError where
+ showsPrec _ (RecConError err) = showString err
+
+-----
+
+data RecUpdError = RecUpdError String
+INSTANCE_TYPEABLE0(RecUpdError,recUpdErrorTc,"RecUpdError")
+
+instance Exception RecUpdError
+
+instance Show RecUpdError where
+ showsPrec _ (RecUpdError err) = showString err
+
+-----
+
+data NoMethodError = NoMethodError String
+INSTANCE_TYPEABLE0(NoMethodError,noMethodErrorTc,"NoMethodError")
+
+instance Exception NoMethodError
+
+instance Show NoMethodError where
+ showsPrec _ (NoMethodError err) = showString err
+
+-----
+
+data AssertionFailed = AssertionFailed String
+INSTANCE_TYPEABLE0(AssertionFailed,assertionFailedTc,"AssertionFailed")
+
+instance Exception AssertionFailed
+
+instance Show AssertionFailed where
+ showsPrec _ (AssertionFailed err) = showString err
+
+-----
+
+data NonTermination = NonTermination
+INSTANCE_TYPEABLE0(NonTermination,nonTerminationTc,"NonTermination")
+
+instance Exception NonTermination
+
+instance Show NonTermination where
+ showsPrec _ NonTermination = showString "<<loop>>"
+
+-- GHC's RTS calls this
+nonTermination :: SomeException
+nonTermination = toException NonTermination
+
+-----
+
+data Deadlock = Deadlock
+INSTANCE_TYPEABLE0(Deadlock,deadlockTc,"Deadlock")
+
+instance Exception Deadlock
+
+instance Show Deadlock where
+ showsPrec _ Deadlock = showString "<<deadlock>>"
+
+-----
+
+data NestedAtomically = NestedAtomically
+INSTANCE_TYPEABLE0(NestedAtomically,nestedAtomicallyTc,"NestedAtomically")
+
+instance Exception NestedAtomically
+
+instance Show NestedAtomically where
+ showsPrec _ NestedAtomically = showString "Control.Concurrent.STM.atomically was nested"
+
+-- GHC's RTS calls this
+nestedAtomically :: SomeException
+nestedAtomically = toException NestedAtomically
+
+-----
+
+instance Exception Dynamic
+
+-----
+
+assertError :: Addr# -> Bool -> a -> a
+assertError str pred v
+ | pred = v
+ | otherwise = throw (AssertionFailed (untangle str "Assertion failed"))
+
+{-
+(untangle coded message) expects "coded" to be of the form
+ "location|details"
+It prints
+ location message details
+-}
+untangle :: Addr# -> String -> String
+untangle coded message
+ = location
+ ++ ": "
+ ++ message
+ ++ details
+ ++ "\n"
+ where
+ coded_str = unpackCStringUtf8# coded
+
+ (location, details)
+ = case (span not_bar coded_str) of { (loc, rest) ->
+ case rest of
+ ('|':det) -> (loc, ' ' : det)
+ _ -> (loc, "")
+ }
+ not_bar c = c /= '|'
+
+-- XXX From GHC.Conc
+throwTo :: Exception e => ThreadId -> e -> IO ()
+throwTo (ThreadId id) ex = IO $ \ s ->
+ case (killThread# id (toException ex) s) of s1 -> (# s1, () #)
+
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