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 | None |
Language | Haskell2010 |
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
- data AsyncException
- data ArrayException
- interruptible :: IO a -> IO a
- data MaskingState
- data IOException
- throw :: Exception e => e -> a
- class (Typeable e, Show e) => Exception e where
- data ErrorCall where
- data ArithException
- data SomeException where
- throwIO :: (Basic1 m, Base m ~ IO, Exception e) => e -> m a
- ioError :: (Basic1 m, Base m ~ IO) => IOError -> m a
- throwTo :: (Basic1 m, Base m ~ IO, Exception e) => ThreadId -> e -> m ()
- catch :: (MonadBaseControl m, Base m ~ IO, Exception e) => m a -> (e -> m a) -> m a
- catches :: (MonadBaseControl m, Base m ~ IO) => m a -> [Handler m a] -> m a
- data Handler m a = Exception e => Handler (e -> m a)
- catchJust :: (MonadBaseControl m, Base m ~ IO, Exception e) => (e -> Maybe b) -> m a -> (b -> m a) -> m a
- handle :: (MonadBaseControl m, Base m ~ IO, Exception e) => (e -> m a) -> m a -> m a
- handleJust :: (MonadBaseControl m, Base m ~ IO, Exception e) => (e -> Maybe b) -> (b -> m a) -> m a -> m a
- try :: (MonadBaseControl m, Base m ~ IO, Exception e) => m a -> m (Either e a)
- tryJust :: (MonadBaseControl m, Base m ~ IO, Exception e) => (e -> Maybe b) -> m a -> m (Either b a)
- evaluate :: (Basic1 m, Base m ~ IO) => a -> m a
- allowInterrupt :: (Basic1 m, Base m ~ IO) => m ()
- bracket :: (MonadBaseControl m, Base m ~ IO) => m a -> (a -> m b) -> (a -> m c) -> m c
- bracket_ :: (MonadBaseControl m, Base m ~ IO) => m a -> m b -> m c -> m c
- bracketOnError :: (MonadBaseControl m, Base m ~ IO) => m a -> (a -> m b) -> (a -> m c) -> m c
- finally :: (MonadBaseControl m, Base m ~ IO) => m a -> m b -> m a
- onException :: (MonadBaseControl m, Base m ~ IO) => 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 TVar
s 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 :: 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 | |
Defined in GHC.IO.Exception Methods (==) :: AsyncException -> AsyncException -> Bool # (/=) :: AsyncException -> AsyncException -> Bool # | |
Ord AsyncException | |
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 | |
Defined in GHC.IO.Exception Methods (==) :: ArrayException -> ArrayException -> Bool # (/=) :: ArrayException -> ArrayException -> Bool # | |
Ord ArrayException | |
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 | |
Defined in GHC.IO | |
Show MaskingState | |
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 # |
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.
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
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
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 | |
Ord ErrorCall | |
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 # |
data ArithException #
Arithmetic exceptions.
Constructors
Overflow | |
Underflow | |
LossOfPrecision | |
DivideByZero | |
Denormal | |
RatioZeroDenominator | Since: base-4.6.0.0 |
Instances
Eq ArithException | |
Defined in GHC.Exception Methods (==) :: ArithException -> ArithException -> Bool # (/=) :: ArithException -> ArithException -> Bool # | |
Ord ArithException | |
Defined in GHC.Exception 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 Methods showsPrec :: Int -> ArithException -> ShowS # show :: ArithException -> String # showList :: [ArithException] -> ShowS # | |
Exception ArithException | Since: base-4.0.0.0 |
Defined in GHC.Exception 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 :: SomeException |
Instances
Show SomeException | Since: base-3.0 |
Defined in GHC.Exception Methods showsPrec :: Int -> SomeException -> ShowS # show :: SomeException -> String # showList :: [SomeException] -> ShowS # | |
Exception SomeException | Since: base-3.0 |
Defined in GHC.Exception Methods toException :: SomeException -> SomeException # fromException :: SomeException -> Maybe SomeException # displayException :: SomeException -> String # |
Throwing exceptions
throwTo :: (Basic1 m, Base m ~ IO, Exception e) => ThreadId -> e -> m () Source #
Generalized version of throwTo
.
Catching exceptions
The catch
functions
Arguments
:: (MonadBaseControl m, Base m ~ IO, 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 m, Base m ~ IO) => m a -> [Handler m a] -> m a Source #
Generalized version of catches
.
Note, when the given computation throws an exception any monadic
side effects in m
will be discarded.
Generalized version of Handler
.
Arguments
:: (MonadBaseControl m, Base m ~ IO, 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 m, Base m ~ IO, Exception e) => (e -> m a) -> m a -> m a Source #
Generalized version of handle
.
Note, when the given computation throws an exception any monadic
side effects in m
will be discarded.
handleJust :: (MonadBaseControl m, Base m ~ IO, Exception e) => (e -> Maybe b) -> (b -> m a) -> m a -> m a Source #
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 m, Base m ~ IO, Exception e) => m a -> m (Either e a) Source #
Generalized version of try
.
Note, when the given computation throws an exception any monadic
side effects in m
will be discarded.
tryJust :: (MonadBaseControl m, Base m ~ IO, Exception e) => (e -> Maybe b) -> m a -> m (Either b a) Source #
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.
allowInterrupt :: (Basic1 m, Base m ~ IO) => m () Source #
Generalized version of allowInterrupt
.
Brackets
Arguments
:: (MonadBaseControl m, Base m ~ IO) | |
=> 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 m, Base m ~ IO) | |
=> 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 m, Base m ~ IO) | |
=> 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 m, Base m ~ IO) | |
=> 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 m, Base m ~ IO) => m a -> m b -> m a Source #
Generalized version of onException
.
Note, any monadic side effects in m
of the "afterward"
computation will be discarded.