Portability | non-portable (extended exceptions) |
---|---|

Stability | experimental |

Maintainer | Bas van Dijk <v.dijk.bas@gmail.com> |

Safe Haskell | Trustworthy |

This is a wrapped version of Control.Exception with types generalized
from `IO`

to all monads in either `MonadBase`

or `MonadBaseControl`

.

- module Control.Exception
- 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 = forall e . 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

module Control.Exception

# Throwing exceptions

throwTo :: (MonadBase IO m, Exception e) => ThreadId -> e -> m ()Source

Generalized version of `throwTo`

.

# Catching exceptions

## The `catch`

functions

:: (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 aSource

Generalized version of `catches`

.

Note, when the given computation throws an exception any monadic
side effects in `m`

will be discarded.

:: (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 aSource

Generalized version of `handle`

.

`m`

will be discarded.

handleJust :: (MonadBaseControl IO m, Exception e) => (e -> Maybe b) -> (b -> m a) -> m a -> m aSource

Generalized version of `handleJust`

.

`m`

will be discarded.

## The `try`

functions

try :: (MonadBaseControl IO m, Exception e) => m a -> m (Either e a)Source

Generalized version of `try`

.

`m`

will be discarded.

tryJust :: (MonadBaseControl IO m, Exception e) => (e -> Maybe b) -> m a -> m (Either b a)Source

Generalized version of `tryJust`

.

`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 bSource

Generalized version of `mask`

.

mask_ :: MonadBaseControl IO m => m a -> m aSource

Generalized version of `mask_`

.

uninterruptibleMask :: MonadBaseControl IO m => ((forall a. m a -> m a) -> m b) -> m bSource

Generalized version of `uninterruptibleMask`

.

uninterruptibleMask_ :: MonadBaseControl IO m => m a -> m aSource

Generalized version of `uninterruptibleMask_`

.

getMaskingState :: MonadBase IO m => m MaskingStateSource

Generalized version of `getMaskingState`

.

allowInterrupt :: MonadBase IO m => m ()Source

Generalized version of `allowInterrupt`

.

# Brackets

:: 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 in`IO`

.

Note that when your `acquire`

and `release`

computations are of type `IO`

it will be more efficient to write:

`liftBaseOp`

(`bracket`

acquire release)

:: 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)

:: 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 in`IO`

.

Note that when your `acquire`

and `release`

computations are of
type `IO`

it will be more efficient to write:

`liftBaseOp`

(`bracketOnError`

acquire release)

# Utilities

:: 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 aSource

Generalized version of `onException`

.

Note, any monadic side effects in `m`

of the "afterward"
computation will be discarded.