Control.Eff.Exception

Exception-producing and exception-handling effects

Documentation

newtype Exc e v

These are exceptions of the type e. This is akin to the error monad.

Constructors

Exc e

Instances

Functor (Exc e)

Typeable (* -> * -> *) Exc

type Fail = Exc ()

throwExc :: (Typeable e, Member (Exc e) r) => e -> Eff r a

Throw an exception in an effectful computation.

die :: Member Fail r => Eff r a

Makes an effect fail, preventing future effects from happening.

runExc :: Typeable e => Eff (Exc e :> r) a -> Eff r (Either e a)

Run a computation that might produce an exception.

runFail :: Eff (Fail :> r) a -> Eff r (Maybe a)

Runs a failable effect, such that failed computation return Nothing, and Just the return value on success.

catchExc :: (Typeable e, Member (Exc e) r) => Eff r a -> (e -> Eff r a) -> Eff r a

Run a computation that might produce exceptions, and give it a way to deal with the exceptions that come up.

onFail

Arguments

:: 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.

rethrowExc :: (Typeable e, Typeable e', Member (Exc e') r) => (e -> e') -> Eff (Exc e :> r) a -> Eff r a

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

liftEither :: (Typeable e, Member (Exc e) r) => Either e a -> Eff r a

Treat Lefts as exceptions and Rights as return values.

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

liftEither in a lifted Monad

liftMaybe :: Member Fail r => Maybe a -> Eff r a

Lift a maybe into the Fail effect, causing failure if it's Nothing.

ignoreFail :: Eff (Fail :> r) a -> Eff r ()

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.