Safe Haskell | Safe |
---|---|

Language | Haskell2010 |

Exception-producing and exception-handling effects

- newtype Exc e v = Exc e
- type Fail = Exc ()
- throwError :: Member (Exc e) r => e -> Eff r a
- throwError_ :: Member (Exc e) r => e -> Eff r ()
- die :: Member Fail r => Eff r a
- runError :: Eff (Exc e ': r) a -> Eff r (Either e a)
- runFail :: Eff (Fail ': r) a -> Eff r (Maybe a)
- catchError :: Member (Exc e) r => Eff r a -> (e -> Eff r a) -> Eff r a
- onFail :: Eff (Fail ': r) a -> Eff r a -> Eff r a
- rethrowError :: Member (Exc e') r => (e -> e') -> Eff (Exc e ': r) a -> Eff r a
- liftEither :: Member (Exc e) r => Either e a -> Eff r a
- liftEitherM :: (Member (Exc e) r, SetMember Lift (Lift m) r) => m (Either e a) -> Eff r a
- liftMaybe :: Member Fail r => Maybe a -> Eff r a
- liftMaybeM :: (Member Fail r, SetMember Lift (Lift m) r) => m (Maybe a) -> Eff r a
- ignoreFail :: Eff (Fail ': r) a -> Eff r ()

# Documentation

Exceptions

exceptions of the type e; no resumption

Exc e |

throwError :: Member (Exc e) r => e -> Eff r a Source #

Throw an exception in an effectful computation. The type is inferred.

throwError_ :: Member (Exc e) r => e -> Eff r () Source #

Throw an exception in an effectful computation. The type is unit, which suppresses the ghc-mod warning "A do-notation statement discarded a result of type"

die :: Member Fail r => Eff r a Source #

Makes an effect fail, preventing future effects from happening.

runError :: Eff (Exc e ': r) a -> Eff r (Either e a) Source #

Run a computation that might produce an exception.

catchError :: Member (Exc e) r => Eff r a -> (e -> Eff r a) -> Eff r a Source #

Run a computation that might produce exceptions, and give it a way to deal with the exceptions that come up. The handler is allowed to rethrow the exception

:: Eff (Fail ': r) a | The fallible computation. |

-> Eff r a | The computation to run on failure. |

-> Eff r a |

Add a default value (i.e. failure handler) to a fallible computation. This hides the fact that a failure happened.

rethrowError :: Member (Exc e') r => (e -> e') -> Eff (Exc e ': r) a -> Eff r a Source #

Run a computation until it produces an exception, and convert and throw that exception in a new context.

liftEither :: Member (Exc e) r => Either e a -> Eff r a Source #

Treat Lefts as exceptions and Rights as return values.

liftEitherM :: (Member (Exc e) r, SetMember Lift (Lift m) r) => m (Either e a) -> Eff r a Source #

`liftEither`

in a lifted Monad

liftMaybeM :: (Member Fail r, SetMember Lift (Lift m) r) => m (Maybe a) -> Eff r a Source #

`liftMaybe`

in a lifted Monad

ignoreFail :: Eff (Fail ': r) a -> Eff r () Source #

Ignores a failure event. Since the event can fail, you cannot inspect its
return type, because it has none on failure. To inspect it, use `runFail`

.