| Copyright | Bas van Dijk Anders Kaseorg |
|---|---|
| License | BSD-style |
| Maintainer | Bas van Dijk <v.dijk.bas@gmail.com> |
| Stability | experimental |
| Portability | non-portable (extended exceptions) |
| Safe Haskell | Trustworthy |
| Language | Haskell98 |
Control.Exception.Lifted
Contents
Description
This is a wrapped version of Control.Exception with types generalized
from IO to all monads in either MonadBase or MonadBaseControl.
Synopsis
- assert :: Bool -> a -> a
- mapException :: (Exception e1, Exception e2) => (e1 -> e2) -> a -> a
- newtype PatternMatchFail = PatternMatchFail String
- newtype RecSelError = RecSelError String
- newtype RecConError = RecConError String
- newtype RecUpdError = RecUpdError String
- newtype NoMethodError = NoMethodError String
- newtype TypeError = TypeError String
- data NonTermination = NonTermination
- data NestedAtomically = NestedAtomically
- asyncExceptionFromException :: Exception e => SomeException -> Maybe e
- asyncExceptionToException :: Exception e => e -> SomeException
- data BlockedIndefinitelyOnMVar = BlockedIndefinitelyOnMVar
- data BlockedIndefinitelyOnSTM = BlockedIndefinitelyOnSTM
- data Deadlock = Deadlock
- data AllocationLimitExceeded = AllocationLimitExceeded
- newtype CompactionFailed = CompactionFailed String
- newtype AssertionFailed = AssertionFailed String
- data SomeAsyncException where
- SomeAsyncException :: forall e. Exception e => e -> SomeAsyncException
- data AsyncException
- data ArrayException
- interruptible :: IO a -> IO a
- data MaskingState
- data IOException
- throw :: Exception e => e -> a
- data ErrorCall where
- class (Typeable e, Show e) => Exception e where
- toException :: e -> SomeException
- fromException :: SomeException -> Maybe e
- displayException :: e -> String
- data ArithException
- data SomeException where
- SomeException :: forall e. Exception e => e -> SomeException
- throwIO :: (MonadBase IO m, Exception e) => e -> m a
- ioError :: MonadBase IO m => IOError -> m a
- throwTo :: (MonadBase IO m, Exception e) => ThreadId -> e -> m ()
- catch :: (MonadBaseControl IO m, Exception e) => m a -> (e -> m a) -> m a
- catches :: MonadBaseControl IO m => m a -> [Handler m a] -> m a
- data Handler m a = Exception e => Handler (e -> m a)
- catchJust :: (MonadBaseControl IO m, Exception e) => (e -> Maybe b) -> m a -> (b -> m a) -> m a
- handle :: (MonadBaseControl IO m, Exception e) => (e -> m a) -> m a -> m a
- handleJust :: (MonadBaseControl IO m, Exception e) => (e -> Maybe b) -> (b -> m a) -> m a -> m a
- try :: (MonadBaseControl IO m, Exception e) => m a -> m (Either e a)
- tryJust :: (MonadBaseControl IO m, Exception e) => (e -> Maybe b) -> m a -> m (Either b a)
- evaluate :: MonadBase IO m => a -> m a
- mask :: MonadBaseControl IO m => ((forall a. m a -> m a) -> m b) -> m b
- mask_ :: MonadBaseControl IO m => m a -> m a
- uninterruptibleMask :: MonadBaseControl IO m => ((forall a. m a -> m a) -> m b) -> m b
- uninterruptibleMask_ :: MonadBaseControl IO m => m a -> m a
- getMaskingState :: MonadBase IO m => m MaskingState
- allowInterrupt :: MonadBase IO m => m ()
- bracket :: MonadBaseControl IO m => m a -> (a -> m b) -> (a -> m c) -> m c
- bracket_ :: MonadBaseControl IO m => m a -> m b -> m c -> m c
- bracketOnError :: MonadBaseControl IO m => m a -> (a -> m b) -> (a -> m c) -> m c
- finally :: MonadBaseControl IO m => m a -> m b -> m a
- onException :: MonadBaseControl IO m => m a -> m b -> m a
Documentation
If the first argument evaluates to True, then the result is the
second argument. Otherwise an AssertionFailed exception is raised,
containing a String with the source file and line number of the
call to assert.
Assertions can normally be turned on or off with a compiler flag
(for GHC, assertions are normally on unless optimisation is turned on
with -O or the -fignore-asserts
option is given). When assertions are turned off, the first
argument to assert is ignored, and the second argument is
returned as the result.
mapException :: (Exception e1, Exception e2) => (e1 -> e2) -> a -> a #
This function maps one exception into another as proposed in the paper "A semantics for imprecise exceptions".
newtype PatternMatchFail #
A pattern match failed. The String gives information about the
source location of the pattern.
Constructors
| PatternMatchFail String |
Instances
| Show PatternMatchFail | Since: base-4.0 |
Defined in Control.Exception.Base Methods showsPrec :: Int -> PatternMatchFail -> ShowS # show :: PatternMatchFail -> String # showList :: [PatternMatchFail] -> ShowS # | |
| Exception PatternMatchFail | Since: base-4.0 |
Defined in Control.Exception.Base Methods toException :: PatternMatchFail -> SomeException # | |
newtype RecSelError #
A record selector was applied to a constructor without the
appropriate field. This can only happen with a datatype with
multiple constructors, where some fields are in one constructor
but not another. The String gives information about the source
location of the record selector.
Constructors
| RecSelError String |
Instances
| Show RecSelError | Since: base-4.0 |
Defined in Control.Exception.Base Methods showsPrec :: Int -> RecSelError -> ShowS # show :: RecSelError -> String # showList :: [RecSelError] -> ShowS # | |
| Exception RecSelError | Since: base-4.0 |
Defined in Control.Exception.Base Methods toException :: RecSelError -> SomeException # fromException :: SomeException -> Maybe RecSelError # displayException :: RecSelError -> String # | |
newtype RecConError #
An uninitialised record field was used. The String gives
information about the source location where the record was
constructed.
Constructors
| RecConError String |
Instances
| Show RecConError | Since: base-4.0 |
Defined in Control.Exception.Base Methods showsPrec :: Int -> RecConError -> ShowS # show :: RecConError -> String # showList :: [RecConError] -> ShowS # | |
| Exception RecConError | Since: base-4.0 |
Defined in Control.Exception.Base Methods toException :: RecConError -> SomeException # fromException :: SomeException -> Maybe RecConError # displayException :: RecConError -> String # | |
newtype RecUpdError #
A record update was performed on a constructor without the
appropriate field. This can only happen with a datatype with
multiple constructors, where some fields are in one constructor
but not another. The String gives information about the source
location of the record update.
Constructors
| RecUpdError String |
Instances
| Show RecUpdError | Since: base-4.0 |
Defined in Control.Exception.Base Methods showsPrec :: Int -> RecUpdError -> ShowS # show :: RecUpdError -> String # showList :: [RecUpdError] -> ShowS # | |
| Exception RecUpdError | Since: base-4.0 |
Defined in Control.Exception.Base Methods toException :: RecUpdError -> SomeException # fromException :: SomeException -> Maybe RecUpdError # displayException :: RecUpdError -> String # | |
newtype NoMethodError #
A class method without a definition (neither a default definition,
nor a definition in the appropriate instance) was called. The
String gives information about which method it was.
Constructors
| NoMethodError String |
Instances
| Show NoMethodError | Since: base-4.0 |
Defined in Control.Exception.Base Methods showsPrec :: Int -> NoMethodError -> ShowS # show :: NoMethodError -> String # showList :: [NoMethodError] -> ShowS # | |
| Exception NoMethodError | Since: base-4.0 |
Defined in Control.Exception.Base Methods toException :: NoMethodError -> SomeException # fromException :: SomeException -> Maybe NoMethodError # displayException :: NoMethodError -> String # | |
An expression that didn't typecheck during compile time was called.
This is only possible with -fdefer-type-errors. The String gives
details about the failed type check.
Since: base-4.9.0.0
Instances
| Show TypeError | Since: base-4.9.0.0 |
| Exception TypeError | Since: base-4.9.0.0 |
Defined in Control.Exception.Base Methods toException :: TypeError -> SomeException # fromException :: SomeException -> Maybe TypeError # displayException :: TypeError -> String # | |
data NonTermination #
Thrown when the runtime system detects that the computation is guaranteed not to terminate. Note that there is no guarantee that the runtime system will notice whether any given computation is guaranteed to terminate or not.
Constructors
| NonTermination |
Instances
| Show NonTermination | Since: base-4.0 |
Defined in Control.Exception.Base Methods showsPrec :: Int -> NonTermination -> ShowS # show :: NonTermination -> String # showList :: [NonTermination] -> ShowS # | |
| Exception NonTermination | Since: base-4.0 |
Defined in Control.Exception.Base Methods toException :: NonTermination -> SomeException # | |
data NestedAtomically #
Thrown when the program attempts to call atomically, from the stm
package, inside another call to atomically.
Constructors
| NestedAtomically |
Instances
| Show NestedAtomically | Since: base-4.0 |
Defined in Control.Exception.Base Methods showsPrec :: Int -> NestedAtomically -> ShowS # show :: NestedAtomically -> String # showList :: [NestedAtomically] -> ShowS # | |
| Exception NestedAtomically | Since: base-4.0 |
Defined in Control.Exception.Base Methods toException :: NestedAtomically -> SomeException # | |
asyncExceptionFromException :: Exception e => SomeException -> Maybe e #
Since: base-4.7.0.0
asyncExceptionToException :: Exception e => e -> SomeException #
Since: base-4.7.0.0
data BlockedIndefinitelyOnMVar #
The thread is blocked on an MVar, but there are no other references
to the MVar so it can't ever continue.
Constructors
| BlockedIndefinitelyOnMVar |
Instances
| Show BlockedIndefinitelyOnMVar | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception Methods showsPrec :: Int -> BlockedIndefinitelyOnMVar -> ShowS # show :: BlockedIndefinitelyOnMVar -> String # showList :: [BlockedIndefinitelyOnMVar] -> ShowS # | |
| Exception BlockedIndefinitelyOnMVar | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception | |
data BlockedIndefinitelyOnSTM #
The thread is waiting to retry an STM transaction, but there are no
other references to any TVars involved, so it can't ever continue.
Constructors
| BlockedIndefinitelyOnSTM |
Instances
| Show BlockedIndefinitelyOnSTM | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception Methods showsPrec :: Int -> BlockedIndefinitelyOnSTM -> ShowS # show :: BlockedIndefinitelyOnSTM -> String # showList :: [BlockedIndefinitelyOnSTM] -> ShowS # | |
| Exception BlockedIndefinitelyOnSTM | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception | |
There are no runnable threads, so the program is deadlocked.
The Deadlock exception is raised in the main thread only.
Constructors
| Deadlock |
Instances
| Show Deadlock | Since: base-4.1.0.0 |
| Exception Deadlock | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception Methods toException :: Deadlock -> SomeException # fromException :: SomeException -> Maybe Deadlock # displayException :: Deadlock -> String # | |
data AllocationLimitExceeded #
This thread has exceeded its allocation limit. See
setAllocationCounter and
enableAllocationLimit.
Since: base-4.8.0.0
Constructors
| AllocationLimitExceeded |
Instances
| Show AllocationLimitExceeded | Since: base-4.7.1.0 |
Defined in GHC.IO.Exception Methods showsPrec :: Int -> AllocationLimitExceeded -> ShowS # show :: AllocationLimitExceeded -> String # showList :: [AllocationLimitExceeded] -> ShowS # | |
| Exception AllocationLimitExceeded | Since: base-4.8.0.0 |
Defined in GHC.IO.Exception | |
newtype CompactionFailed #
Compaction found an object that cannot be compacted. Functions
cannot be compacted, nor can mutable objects or pinned objects.
See compact.
Since: base-4.10.0.0
Constructors
| CompactionFailed String |
Instances
| Show CompactionFailed | Since: base-4.10.0.0 |
Defined in GHC.IO.Exception Methods showsPrec :: Int -> CompactionFailed -> ShowS # show :: CompactionFailed -> String # showList :: [CompactionFailed] -> ShowS # | |
| Exception CompactionFailed | Since: base-4.10.0.0 |
Defined in GHC.IO.Exception Methods toException :: CompactionFailed -> SomeException # | |
newtype AssertionFailed #
Constructors
| AssertionFailed String |
Instances
| Show AssertionFailed | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception Methods showsPrec :: Int -> AssertionFailed -> ShowS # show :: AssertionFailed -> String # showList :: [AssertionFailed] -> ShowS # | |
| Exception AssertionFailed | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception Methods toException :: AssertionFailed -> SomeException # | |
data SomeAsyncException where #
Superclass for asynchronous exceptions.
Since: base-4.7.0.0
Constructors
| SomeAsyncException :: forall e. Exception e => e -> SomeAsyncException |
Instances
| Show SomeAsyncException | Since: base-4.7.0.0 |
Defined in GHC.IO.Exception Methods showsPrec :: Int -> SomeAsyncException -> ShowS # show :: SomeAsyncException -> String # showList :: [SomeAsyncException] -> ShowS # | |
| Exception SomeAsyncException | Since: base-4.7.0.0 |
Defined in GHC.IO.Exception Methods toException :: SomeAsyncException -> SomeException # fromException :: SomeException -> Maybe SomeAsyncException # | |
data AsyncException #
Asynchronous exceptions.
Constructors
| StackOverflow | The current thread's stack exceeded its limit. Since an exception has been raised, the thread's stack will certainly be below its limit again, but the programmer should take remedial action immediately. |
| HeapOverflow | The program's heap is reaching its limit, and the program should take action to reduce the amount of live data it has. Notes:
|
| ThreadKilled | This exception is raised by another thread
calling |
| UserInterrupt | This exception is raised by default in the main thread of the program when the user requests to terminate the program via the usual mechanism(s) (e.g. Control-C in the console). |
Instances
| Eq AsyncException | Since: base-4.2.0.0 |
Defined in GHC.IO.Exception Methods (==) :: AsyncException -> AsyncException -> Bool # (/=) :: AsyncException -> AsyncException -> Bool # | |
| Ord AsyncException | Since: base-4.2.0.0 |
Defined in GHC.IO.Exception Methods compare :: AsyncException -> AsyncException -> Ordering # (<) :: AsyncException -> AsyncException -> Bool # (<=) :: AsyncException -> AsyncException -> Bool # (>) :: AsyncException -> AsyncException -> Bool # (>=) :: AsyncException -> AsyncException -> Bool # max :: AsyncException -> AsyncException -> AsyncException # min :: AsyncException -> AsyncException -> AsyncException # | |
| Show AsyncException | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception Methods showsPrec :: Int -> AsyncException -> ShowS # show :: AsyncException -> String # showList :: [AsyncException] -> ShowS # | |
| Exception AsyncException | Since: base-4.7.0.0 |
Defined in GHC.IO.Exception Methods toException :: AsyncException -> SomeException # | |
data ArrayException #
Exceptions generated by array operations
Constructors
| IndexOutOfBounds String | An attempt was made to index an array outside its declared bounds. |
| UndefinedElement String | An attempt was made to evaluate an element of an array that had not been initialized. |
Instances
| Eq ArrayException | Since: base-4.2.0.0 |
Defined in GHC.IO.Exception Methods (==) :: ArrayException -> ArrayException -> Bool # (/=) :: ArrayException -> ArrayException -> Bool # | |
| Ord ArrayException | Since: base-4.2.0.0 |
Defined in GHC.IO.Exception Methods compare :: ArrayException -> ArrayException -> Ordering # (<) :: ArrayException -> ArrayException -> Bool # (<=) :: ArrayException -> ArrayException -> Bool # (>) :: ArrayException -> ArrayException -> Bool # (>=) :: ArrayException -> ArrayException -> Bool # max :: ArrayException -> ArrayException -> ArrayException # min :: ArrayException -> ArrayException -> ArrayException # | |
| Show ArrayException | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception Methods showsPrec :: Int -> ArrayException -> ShowS # show :: ArrayException -> String # showList :: [ArrayException] -> ShowS # | |
| Exception ArrayException | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception Methods toException :: ArrayException -> SomeException # | |
interruptible :: IO a -> IO a #
Allow asynchronous exceptions to be raised even inside mask, making
the operation interruptible (see the discussion of "Interruptible operations"
in Exception).
When called outside mask, or inside uninterruptibleMask, this
function has no effect.
Since: base-4.9.0.0
data MaskingState #
Describes the behaviour of a thread when an asynchronous exception is received.
Constructors
| Unmasked | asynchronous exceptions are unmasked (the normal state) |
| MaskedInterruptible | the state during |
| MaskedUninterruptible | the state during |
Instances
| Eq MaskingState | Since: base-4.3.0.0 |
Defined in GHC.IO | |
| Show MaskingState | Since: base-4.3.0.0 |
Defined in GHC.IO Methods showsPrec :: Int -> MaskingState -> ShowS # show :: MaskingState -> String # showList :: [MaskingState] -> ShowS # | |
data IOException #
Exceptions that occur in the IO monad.
An IOException records a more specific error type, a descriptive
string and maybe the handle that was used when the error was
flagged.
Instances
| Eq IOException | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception | |
| Show IOException | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception Methods showsPrec :: Int -> IOException -> ShowS # show :: IOException -> String # showList :: [IOException] -> ShowS # | |
| Exception IOException | Since: base-4.1.0.0 |
Defined in GHC.IO.Exception Methods toException :: IOException -> SomeException # fromException :: SomeException -> Maybe IOException # displayException :: IOException -> String # | |
| Error IOException | |
Defined in Control.Monad.Trans.Error | |
throw :: Exception e => e -> a #
Throw an exception. Exceptions may be thrown from purely
functional code, but may only be caught within the IO monad.
This is thrown when the user calls error. The first String is the
argument given to error, second String is the location.
Constructors
| ErrorCallWithLocation String String |
Instances
| Eq ErrorCall | Since: base-4.7.0.0 |
| Ord ErrorCall | Since: base-4.7.0.0 |
| Show ErrorCall | Since: base-4.0.0.0 |
| Exception ErrorCall | Since: base-4.0.0.0 |
Defined in GHC.Exception Methods toException :: ErrorCall -> SomeException # fromException :: SomeException -> Maybe ErrorCall # displayException :: ErrorCall -> String # | |
class (Typeable e, Show e) => Exception e where #
Any type that you wish to throw or catch as an exception must be an
instance of the Exception class. The simplest case is a new exception
type directly below the root:
data MyException = ThisException | ThatException
deriving Show
instance Exception MyExceptionThe default method definitions in the Exception class do what we need
in this case. You can now throw and catch ThisException and
ThatException as exceptions:
*Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
Caught ThisException
In more complicated examples, you may wish to define a whole hierarchy of exceptions:
---------------------------------------------------------------------
-- Make the root exception type for all the exceptions in a compiler
data SomeCompilerException = forall e . Exception e => SomeCompilerException e
instance Show SomeCompilerException where
show (SomeCompilerException e) = show e
instance Exception SomeCompilerException
compilerExceptionToException :: Exception e => e -> SomeException
compilerExceptionToException = toException . SomeCompilerException
compilerExceptionFromException :: Exception e => SomeException -> Maybe e
compilerExceptionFromException x = do
SomeCompilerException a <- fromException x
cast a
---------------------------------------------------------------------
-- Make a subhierarchy for exceptions in the frontend of the compiler
data SomeFrontendException = forall e . Exception e => SomeFrontendException e
instance Show SomeFrontendException where
show (SomeFrontendException e) = show e
instance Exception SomeFrontendException where
toException = compilerExceptionToException
fromException = compilerExceptionFromException
frontendExceptionToException :: Exception e => e -> SomeException
frontendExceptionToException = toException . SomeFrontendException
frontendExceptionFromException :: Exception e => SomeException -> Maybe e
frontendExceptionFromException x = do
SomeFrontendException a <- fromException x
cast a
---------------------------------------------------------------------
-- Make an exception type for a particular frontend compiler exception
data MismatchedParentheses = MismatchedParentheses
deriving Show
instance Exception MismatchedParentheses where
toException = frontendExceptionToException
fromException = frontendExceptionFromExceptionWe can now catch a MismatchedParentheses exception as
MismatchedParentheses, SomeFrontendException or
SomeCompilerException, but not other types, e.g. IOException:
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: IOException))
*** Exception: MismatchedParentheses
Minimal complete definition
Nothing
Methods
toException :: e -> SomeException #
fromException :: SomeException -> Maybe e #
displayException :: e -> String #
Render this exception value in a human-friendly manner.
Default implementation: .show
Since: base-4.8.0.0
Instances
data ArithException #
Arithmetic exceptions.
Constructors
| Overflow | |
| Underflow | |
| LossOfPrecision | |
| DivideByZero | |
| Denormal | |
| RatioZeroDenominator | Since: base-4.6.0.0 |
Instances
| Eq ArithException | Since: base-3.0 |
Defined in GHC.Exception.Type Methods (==) :: ArithException -> ArithException -> Bool # (/=) :: ArithException -> ArithException -> Bool # | |
| Ord ArithException | Since: base-3.0 |
Defined in GHC.Exception.Type Methods compare :: ArithException -> ArithException -> Ordering # (<) :: ArithException -> ArithException -> Bool # (<=) :: ArithException -> ArithException -> Bool # (>) :: ArithException -> ArithException -> Bool # (>=) :: ArithException -> ArithException -> Bool # max :: ArithException -> ArithException -> ArithException # min :: ArithException -> ArithException -> ArithException # | |
| Show ArithException | Since: base-4.0.0.0 |
Defined in GHC.Exception.Type Methods showsPrec :: Int -> ArithException -> ShowS # show :: ArithException -> String # showList :: [ArithException] -> ShowS # | |
| Exception ArithException | Since: base-4.0.0.0 |
Defined in GHC.Exception.Type Methods toException :: ArithException -> SomeException # | |
data SomeException where #
The SomeException type is the root of the exception type hierarchy.
When an exception of type e is thrown, behind the scenes it is
encapsulated in a SomeException.
Constructors
| SomeException :: forall e. Exception e => e -> SomeException |
Instances
| Show SomeException | Since: base-3.0 |
Defined in GHC.Exception.Type Methods showsPrec :: Int -> SomeException -> ShowS # show :: SomeException -> String # showList :: [SomeException] -> ShowS # | |
| Exception SomeException | Since: base-3.0 |
Defined in GHC.Exception.Type Methods toException :: SomeException -> SomeException # fromException :: SomeException -> Maybe SomeException # displayException :: SomeException -> String # | |
Throwing exceptions
Catching exceptions
The catch functions
Arguments
| :: (MonadBaseControl IO m, Exception e) | |
| => m a | The computation to run |
| -> (e -> m a) | Handler to invoke if an exception is raised |
| -> m a |
Generalized version of catch.
Note, when the given computation throws an exception any monadic
side effects in m will be discarded.
catches :: MonadBaseControl IO m => m a -> [Handler m a] -> m a #
Generalized version of catches.
Note, when the given computation throws an exception any monadic
side effects in m will be discarded.
Arguments
| :: (MonadBaseControl IO m, Exception e) | |
| => (e -> Maybe b) | Predicate to select exceptions |
| -> m a | Computation to run |
| -> (b -> m a) | Handler |
| -> m a |
Generalized version of catchJust.
Note, when the given computation throws an exception any monadic
side effects in m will be discarded.
The handle functions
handle :: (MonadBaseControl IO m, Exception e) => (e -> m a) -> m a -> m a #
Generalized version of handle.
Note, when the given computation throws an exception any monadic
side effects in m will be discarded.
handleJust :: (MonadBaseControl IO m, Exception e) => (e -> Maybe b) -> (b -> m a) -> m a -> m a #
Generalized version of handleJust.
Note, when the given computation throws an exception any monadic
side effects in m will be discarded.
The try functions
try :: (MonadBaseControl IO m, Exception e) => m a -> m (Either e a) #
Generalized version of try.
Note, when the given computation throws an exception any monadic
side effects in m will be discarded.
tryJust :: (MonadBaseControl IO m, Exception e) => (e -> Maybe b) -> m a -> m (Either b a) #
Generalized version of tryJust.
Note, when the given computation throws an exception any monadic
side effects in m will be discarded.
The evaluate function
Asynchronous Exceptions
Asynchronous exception control
The following functions allow a thread to control delivery of asynchronous exceptions during a critical region.
mask :: MonadBaseControl IO m => ((forall a. m a -> m a) -> m b) -> m b #
Generalized version of mask.
mask_ :: MonadBaseControl IO m => m a -> m a #
Generalized version of mask_.
uninterruptibleMask :: MonadBaseControl IO m => ((forall a. m a -> m a) -> m b) -> m b #
Generalized version of uninterruptibleMask.
uninterruptibleMask_ :: MonadBaseControl IO m => m a -> m a #
Generalized version of uninterruptibleMask_.
getMaskingState :: MonadBase IO m => m MaskingState #
Generalized version of getMaskingState.
allowInterrupt :: MonadBase IO m => m () #
Generalized version of allowInterrupt.
Brackets
Arguments
| :: MonadBaseControl IO m | |
| => m a | computation to run first ("acquire resource") |
| -> (a -> m b) | computation to run last ("release resource") |
| -> (a -> m c) | computation to run in-between |
| -> m c |
Generalized version of bracket.
Note:
- When the "acquire" or "release" computations throw exceptions
any monadic side effects in
mwill be discarded. - When the "in-between" computation throws an exception any
monadic side effects in
mproduced by that computation will be discarded but the side effects of the "acquire" or "release" computations will be retained. - Also, any monadic side effects in
mof the "release" computation will be discarded; it is run only for its side effects inIO.
Note that when your acquire and release computations are of type IO
it will be more efficient to write:
liftBaseOp(bracketacquire release)
Arguments
| :: MonadBaseControl IO m | |
| => m a | computation to run first ("acquire resource") |
| -> m b | computation to run last ("release resource") |
| -> m c | computation to run in-between |
| -> m c |
Generalized version of bracket_.
Note any monadic side effects in m of both the "acquire" and
"release" computations will be discarded. To keep the monadic
side effects of the "acquire" computation, use bracket with
constant functions instead.
Note that when your acquire and release computations are of type IO
it will be more efficient to write:
liftBaseOp_(bracket_acquire release)
Arguments
| :: MonadBaseControl IO m | |
| => m a | computation to run first ("acquire resource") |
| -> (a -> m b) | computation to run last ("release resource") |
| -> (a -> m c) | computation to run in-between |
| -> m c |
Generalized version of bracketOnError.
Note:
- When the "acquire" or "release" computations throw exceptions
any monadic side effects in
mwill be discarded. - When the "in-between" computation throws an exception any
monadic side effects in
mproduced by that computation will be discarded but the side effects of the "acquire" computation will be retained. - Also, any monadic side effects in
mof the "release" computation will be discarded; it is run only for its side effects inIO.
Note that when your acquire and release computations are of
type IO it will be more efficient to write:
liftBaseOp(bracketOnErroracquire release)
Utilities
Arguments
| :: MonadBaseControl IO m | |
| => m a | computation to run first |
| -> m b | computation to run afterward (even if an exception was raised) |
| -> m a |
Generalized version of finally.
Note, any monadic side effects in m of the "afterward"
computation will be discarded.
onException :: MonadBaseControl IO m => m a -> m b -> m a #
Generalized version of onException.
Note, any monadic side effects in m of the "afterward"
computation will be discarded.