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 | Safe |
Language | Haskell98 |
Control.Exception.Lifted
Description
This is a wrapped version of Control.Exception with types generalized
from IO
to all monads in either MonadBase
or MonadBaseControl
.
Synopsis
- data BlockedIndefinitelyOnMVar = BlockedIndefinitelyOnMVar
- assert :: Bool -> a -> a
- newtype TypeError = TypeError String
- data SomeException = (Exception e, HasExceptionContext) => SomeException e
- data ArithException
- data ExceptionWithContext a = ExceptionWithContext ExceptionContext a
- class (Typeable e, Show e) => Exception e where
- toException :: e -> SomeException
- fromException :: SomeException -> Maybe e
- displayException :: e -> String
- backtraceDesired :: e -> Bool
- someExceptionContext :: SomeException -> ExceptionContext
- addExceptionContext :: ExceptionAnnotation a => a -> SomeException -> SomeException
- data ErrorCall where
- throw :: forall a e. (?callStack :: CallStack, Exception e) => e -> a
- data IOException
- data MaskingState
- annotateIO :: ExceptionAnnotation e => e -> IO a -> IO a
- interruptible :: IO a -> IO a
- data ArrayException
- data AsyncException
- data SomeAsyncException = Exception e => SomeAsyncException e
- newtype AssertionFailed = AssertionFailed String
- newtype CompactionFailed = CompactionFailed String
- data AllocationLimitExceeded = AllocationLimitExceeded
- data Deadlock = Deadlock
- data BlockedIndefinitelyOnSTM = BlockedIndefinitelyOnSTM
- asyncExceptionToException :: Exception e => e -> SomeException
- asyncExceptionFromException :: Exception e => SomeException -> Maybe e
- data NestedAtomically = NestedAtomically
- data NonTermination = NonTermination
- newtype NoMethodError = NoMethodError String
- newtype RecUpdError = RecUpdError String
- newtype RecConError = RecConError String
- newtype RecSelError = RecSelError String
- newtype PatternMatchFail = PatternMatchFail String
- mapException :: (Exception e1, Exception e2) => (e1 -> e2) -> a -> a
- 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 :: Type -> Type) 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
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
Exception BlockedIndefinitelyOnMVar | @since base-4.1.0.0 |
Show BlockedIndefinitelyOnMVar | @since base-4.1.0.0 |
Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> BlockedIndefinitelyOnMVar -> ShowS # show :: BlockedIndefinitelyOnMVar -> String # showList :: [BlockedIndefinitelyOnMVar] -> ShowS # |
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.
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
Exception TypeError | @since base-4.9.0.0 |
Defined in GHC.Internal.Control.Exception.Base Methods toException :: TypeError -> SomeException # fromException :: SomeException -> Maybe TypeError # displayException :: TypeError -> String # backtraceDesired :: TypeError -> Bool # | |
Show TypeError | @since base-4.9.0.0 |
data SomeException #
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
(Exception e, HasExceptionContext) => SomeException e |
Instances
Exception SomeException | This drops any attached @since base-3.0 |
Defined in GHC.Internal.Exception.Type Methods toException :: SomeException -> SomeException # fromException :: SomeException -> Maybe SomeException # displayException :: SomeException -> String # backtraceDesired :: SomeException -> Bool # | |
Show SomeException | Since: ghc-internal-3.0 |
Defined in GHC.Internal.Exception.Type Methods showsPrec :: Int -> SomeException -> ShowS # show :: SomeException -> String # showList :: [SomeException] -> ShowS # |
data ArithException #
Arithmetic exceptions.
Constructors
Overflow | |
Underflow | |
LossOfPrecision | |
DivideByZero | |
Denormal | |
RatioZeroDenominator | @since base-4.6.0.0 |
Instances
data ExceptionWithContext a #
Wraps a particular exception exposing its ExceptionContext
. Intended to
be used when catch
ing exceptions in cases where access to the context is
desired.
Constructors
ExceptionWithContext ExceptionContext a |
Instances
Exception a => Exception (ExceptionWithContext a) | |
Defined in GHC.Internal.Exception.Type Methods toException :: ExceptionWithContext a -> SomeException # fromException :: SomeException -> Maybe (ExceptionWithContext a) # displayException :: ExceptionWithContext a -> String # backtraceDesired :: ExceptionWithContext a -> Bool # | |
Show a => Show (ExceptionWithContext a) | |
Defined in GHC.Internal.Exception.Type Methods showsPrec :: Int -> ExceptionWithContext a -> ShowS # show :: ExceptionWithContext a -> String # showList :: [ExceptionWithContext a] -> ShowS # |
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 MyException
The 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 = frontendExceptionFromException
We 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 #
toException
should produce a SomeException
with no attached ExceptionContext
.
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
backtraceDesired :: e -> Bool #
Instances
someExceptionContext :: SomeException -> ExceptionContext #
View the ExceptionContext
of a SomeException
.
addExceptionContext :: ExceptionAnnotation a => a -> SomeException -> SomeException #
Add more ExceptionContext
to a SomeException
.
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
Exception ErrorCall | @since base-4.0.0.0 |
Defined in GHC.Internal.Exception Methods toException :: ErrorCall -> SomeException # fromException :: SomeException -> Maybe ErrorCall # displayException :: ErrorCall -> String # backtraceDesired :: ErrorCall -> Bool # | |
Show ErrorCall | @since base-4.0.0.0 |
Eq ErrorCall | @since base-4.7.0.0 |
Ord ErrorCall | @since base-4.7.0.0 |
throw :: forall a e. (?callStack :: CallStack, Exception e) => e -> a #
Throw an exception. Exceptions may be thrown from purely
functional code, but may only be caught within the IO
monad.
WARNING: You may want to use throwIO
instead so that your pure code
stays exception-free.
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
Exception IOException | @since base-4.1.0.0 |
Defined in GHC.Internal.IO.Exception Methods toException :: IOException -> SomeException # fromException :: SomeException -> Maybe IOException # displayException :: IOException -> String # backtraceDesired :: IOException -> Bool # | |
Show IOException | @since base-4.1.0.0 |
Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> IOException -> ShowS # show :: IOException -> String # showList :: [IOException] -> ShowS # | |
Eq IOException | @since base-4.1.0.0 |
Defined in GHC.Internal.IO.Exception |
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
Show MaskingState | @since base-4.3.0.0 |
Defined in GHC.Internal.IO Methods showsPrec :: Int -> MaskingState -> ShowS # show :: MaskingState -> String # showList :: [MaskingState] -> ShowS # | |
Eq MaskingState | @since base-4.3.0.0 |
Defined in GHC.Internal.IO |
annotateIO :: ExceptionAnnotation e => e -> IO a -> IO a #
Execute an IO
action, adding the given ExceptionContext
to any thrown synchronous exceptions.
@since base-2.20.0.0
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 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
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
data SomeAsyncException #
Superclass for asynchronous exceptions.
@since base-4.7.0.0
Constructors
Exception e => SomeAsyncException e |
Instances
Exception SomeAsyncException | @since base-4.7.0.0 |
Defined in GHC.Internal.IO.Exception Methods toException :: SomeAsyncException -> SomeException # fromException :: SomeException -> Maybe SomeAsyncException # | |
Show SomeAsyncException | @since base-4.7.0.0 |
Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> SomeAsyncException -> ShowS # show :: SomeAsyncException -> String # showList :: [SomeAsyncException] -> ShowS # |
newtype AssertionFailed #
Constructors
AssertionFailed String |
Instances
Exception AssertionFailed | @since base-4.1.0.0 |
Defined in GHC.Internal.IO.Exception Methods toException :: AssertionFailed -> SomeException # fromException :: SomeException -> Maybe AssertionFailed # displayException :: AssertionFailed -> String # backtraceDesired :: AssertionFailed -> Bool # | |
Show AssertionFailed | @since base-4.1.0.0 |
Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> AssertionFailed -> ShowS # show :: AssertionFailed -> String # showList :: [AssertionFailed] -> ShowS # |
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
Exception CompactionFailed | @since base-4.10.0.0 |
Defined in GHC.Internal.IO.Exception Methods toException :: CompactionFailed -> SomeException # fromException :: SomeException -> Maybe CompactionFailed # | |
Show CompactionFailed | @since base-4.10.0.0 |
Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> CompactionFailed -> ShowS # show :: CompactionFailed -> String # showList :: [CompactionFailed] -> ShowS # |
data AllocationLimitExceeded #
This thread has exceeded its allocation limit. See
setAllocationCounter
and
enableAllocationLimit
.
@since base-4.8.0.0
Constructors
AllocationLimitExceeded |
Instances
Exception AllocationLimitExceeded | @since base-4.8.0.0 |
Defined in GHC.Internal.IO.Exception | |
Show AllocationLimitExceeded | @since base-4.7.1.0 |
Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> AllocationLimitExceeded -> ShowS # show :: AllocationLimitExceeded -> String # showList :: [AllocationLimitExceeded] -> ShowS # |
There are no runnable threads, so the program is deadlocked.
The Deadlock
exception is raised in the main thread only.
Constructors
Deadlock |
Instances
Exception Deadlock | @since base-4.1.0.0 |
Defined in GHC.Internal.IO.Exception Methods toException :: Deadlock -> SomeException # fromException :: SomeException -> Maybe Deadlock # displayException :: Deadlock -> String # backtraceDesired :: Deadlock -> Bool # | |
Show Deadlock | @since base-4.1.0.0 |
data BlockedIndefinitelyOnSTM #
The thread is waiting to retry an STM transaction, but there are no
other references to any TVar
s involved, so it can't ever continue.
Constructors
BlockedIndefinitelyOnSTM |
Instances
Exception BlockedIndefinitelyOnSTM | @since base-4.1.0.0 |
Defined in GHC.Internal.IO.Exception | |
Show BlockedIndefinitelyOnSTM | @since base-4.1.0.0 |
Defined in GHC.Internal.IO.Exception Methods showsPrec :: Int -> BlockedIndefinitelyOnSTM -> ShowS # show :: BlockedIndefinitelyOnSTM -> String # showList :: [BlockedIndefinitelyOnSTM] -> ShowS # |
asyncExceptionToException :: Exception e => e -> SomeException #
@since base-4.7.0.0
asyncExceptionFromException :: Exception e => SomeException -> Maybe e #
@since base-4.7.0.0
data NestedAtomically #
Thrown when the program attempts to call atomically
, from the stm
package, inside another call to atomically
.
Constructors
NestedAtomically |
Instances
Exception NestedAtomically | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods toException :: NestedAtomically -> SomeException # fromException :: SomeException -> Maybe NestedAtomically # | |
Show NestedAtomically | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods showsPrec :: Int -> NestedAtomically -> ShowS # show :: NestedAtomically -> String # showList :: [NestedAtomically] -> ShowS # |
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
Exception NonTermination | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods toException :: NonTermination -> SomeException # fromException :: SomeException -> Maybe NonTermination # displayException :: NonTermination -> String # backtraceDesired :: NonTermination -> Bool # | |
Show NonTermination | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods showsPrec :: Int -> NonTermination -> ShowS # show :: NonTermination -> String # showList :: [NonTermination] -> ShowS # |
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
Exception NoMethodError | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods toException :: NoMethodError -> SomeException # fromException :: SomeException -> Maybe NoMethodError # displayException :: NoMethodError -> String # backtraceDesired :: NoMethodError -> Bool # | |
Show NoMethodError | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods showsPrec :: Int -> NoMethodError -> ShowS # show :: NoMethodError -> String # showList :: [NoMethodError] -> ShowS # |
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
Exception RecUpdError | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods toException :: RecUpdError -> SomeException # fromException :: SomeException -> Maybe RecUpdError # displayException :: RecUpdError -> String # backtraceDesired :: RecUpdError -> Bool # | |
Show RecUpdError | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods showsPrec :: Int -> RecUpdError -> ShowS # show :: RecUpdError -> String # showList :: [RecUpdError] -> ShowS # |
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
Exception RecConError | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods toException :: RecConError -> SomeException # fromException :: SomeException -> Maybe RecConError # displayException :: RecConError -> String # backtraceDesired :: RecConError -> Bool # | |
Show RecConError | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods showsPrec :: Int -> RecConError -> ShowS # show :: RecConError -> String # showList :: [RecConError] -> ShowS # |
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
Exception RecSelError | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods toException :: RecSelError -> SomeException # fromException :: SomeException -> Maybe RecSelError # displayException :: RecSelError -> String # backtraceDesired :: RecSelError -> Bool # | |
Show RecSelError | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods showsPrec :: Int -> RecSelError -> ShowS # show :: RecSelError -> String # showList :: [RecSelError] -> ShowS # |
newtype PatternMatchFail #
A pattern match failed. The String
gives information about the
source location of the pattern.
Constructors
PatternMatchFail String |
Instances
Exception PatternMatchFail | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods toException :: PatternMatchFail -> SomeException # fromException :: SomeException -> Maybe PatternMatchFail # | |
Show PatternMatchFail | @since base-4.0 |
Defined in GHC.Internal.Control.Exception.Base Methods showsPrec :: Int -> PatternMatchFail -> ShowS # show :: PatternMatchFail -> String # showList :: [PatternMatchFail] -> ShowS # |
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".
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
m
will be discarded. - When the "in-between" computation throws an exception any
monadic side effects in
m
produced 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
m
of 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
(bracket
acquire 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
m
will be discarded. - When the "in-between" computation throws an exception any
monadic side effects in
m
produced by that computation will be discarded but the side effects of the "acquire" computation will be retained. - Also, any monadic side effects in
m
of 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
(bracketOnError
acquire 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.