LIO.MonadCatch

This module generalizes throw and catch (from Control.Exception) to methods that can be defined on multiple monads.

Documentation

class Monad m => MonadCatch m where

MonadCatch is the class used to generalize the standard IO catch and throwIO functions to methods that can be defined in multiple monads. Minimal definition requires: mask, throwIO, catch, and onException.

Methods

mask

Arguments

:: ((forall a. m a -> m a) -> m b)

Function that takes a mask-restoring function as argument and returns an action to execute.

-> m b

Executes a computation with asynchronous exceptions masked. See Control.Exception for more details.

mask_ :: m a -> m a

Like mask, but does not pass a restore action to the argument.

throwIO :: Exception e => e -> m a

A variant of throwIO that can be used within the monad.

catch

Arguments

:: Exception e

=> m a

Computation to run

-> (e -> m a)

Handler

-> m a

Simplest exception-catching function.

handle :: Exception e => (e -> m a) -> m a -> m a

Version of catch with the arguments swapped around.

onException

Arguments

:: m a

Computation to run first

-> m b

Computation to run after, if an exception was raised.

-> m a

Performs an action and a subsequent action if an exceptino is raised.

bracket

Arguments

:: m b

Computation to run first

-> (b -> m c)

Computation to run last

-> (b -> m a)

Computation to run in-between

-> m a

This function allows you to execute an action with an initial "acquire resource" and final "release resource" as bracket of Control.Exception.

bracket_ :: m a -> m b -> m c -> m c

Variant of bracket where the return value from the first computation is not required.

finally

Arguments

:: m a

Computation to run first

-> m b

Computation to run after

-> m a

Performs an action and a subsequent action.

Instances

MonadCatch IO

LabelState l p s => MonadCatch (LIO l p s)

genericBracket

Arguments

:: MonadCatch m

=> (m b -> m c -> m b)

On exception function

-> m a

Action to perform first

-> (a -> m c)

Action to perform last

-> (a -> m b)

Action to perform in-between

-> m b

Result of in-between action

Given some general onException function, genericBracket allows you to execute an action with an initial "acquire resource" and final "release resource" as bracket of Control.Exception.