Control.Exception.Control

This is a wrapped version of Control.Exception with types generalized from IO to all monads in MonadControlIO.

Documentation

module Control.Exception

Throwing exceptions

throwIO :: (MonadIO m, Exception e) => e -> m α

Generalized version of throwIO.

ioError :: MonadIO m => IOError -> m α

Generalized version of ioError.

Catching exceptions

The catch functions

catch

Arguments

:: (MonadControlIO m, Exception e)

=> m α

The computation to run

-> (e -> m α)

Handler to invoke if an exception is raised

-> m α

Generalized version of catch.

catches :: MonadControlIO m => m α -> [Handler m α] -> m α

Generalized version of catches.

data Handler m α

Generalized version of Handler.

Constructors

forall e . Exception e => Handler (e -> m α)

catchJust

Arguments

:: (MonadControlIO m, Exception e)

=> (e -> Maybe β)

Predicate to select exceptions

-> m α

Computation to run

-> (β -> m α)

Handler

-> m α

Generalized version of catchJust.

The handle functions

handle :: (MonadControlIO m, Exception e) => (e -> m α) -> m α -> m α

Generalized version of handle.

handleJust :: (MonadControlIO m, Exception e) => (e -> Maybe β) -> (β -> m α) -> m α -> m α

Generalized version of handleJust.

The try functions

try :: (MonadControlIO m, Exception e) => m α -> m (Either e α)

Generalized version of try.

tryJust :: (MonadControlIO m, Exception e) => (e -> Maybe β) -> m α -> m (Either β α)

Generalized version of tryJust.

The evaluate function

evaluate :: MonadIO m => α -> m α

Generalized version of evaluate.

Asynchronous Exceptions

Asynchronous exception control

The following functions allow a thread to control delivery of asynchronous exceptions during a critical region.

mask :: MonadControlIO m => ((forall α. m α -> m α) -> m β) -> m β

Generalized version of mask.

mask_ :: MonadControlIO m => m α -> m α

Generalized version of mask_.

uninterruptibleMask :: MonadControlIO m => ((forall α. m α -> m α) -> m β) -> m β

Generalized version of uninterruptibleMask.

uninterruptibleMask_ :: MonadControlIO m => m α -> m α

Generalized version of uninterruptibleMask_.

getMaskingState :: MonadIO m => m MaskingState

Generalized version of getMaskingState.

Brackets

bracket

Arguments

:: MonadControlIO m

=> m α

computation to run first ("acquire resource")

-> (α -> m β)

computation to run last ("release resource")

-> (α -> m γ)

computation to run in-between

-> m γ

Generalized version of bracket. Note, any monadic side effects in m of the "release" computation will be discarded; it is run only for its side effects in IO.

Note that when your acquire and release computations are of type IO it will be more efficient to write:

liftIOOp (bracket acquire release)

bracket_

Arguments

:: MonadControlIO m

=> m α

computation to run first ("acquire resource")

-> m β

computation to run last ("release resource")

-> m γ

computation to run in-between

-> m γ

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:

liftIOOp_ (bracket_ acquire release)

bracketOnError

Arguments

:: MonadControlIO m

=> m α

computation to run first ("acquire resource")

-> (α -> m β)

computation to run last ("release resource")

-> (α -> m γ)

computation to run in-between

-> m γ

Generalized version of bracketOnError. Note, any monadic side effects in m of the "release" computation will be discarded.

Note that when your acquire and release computations are of type IO it will be more efficient to write:

liftIOOp (bracketOnError acquire release)

Utilities

finally

Arguments

:: MonadControlIO m

=> m α

computation to run first

-> m β

computation to run afterward (even if an exception was raised)

-> m α

Generalized version of finally. Note, any monadic side effects in m of the "afterward" computation will be discarded.

onException :: MonadControlIO m => m α -> m β -> m α

Generalized version of onException. Note, any monadic side effects in m of the "afterward" computation will be discarded.