Control.Eff.Exception

Exception-producing and exception-handling effects

Documentation

newtype Exc e v

Exceptions

exceptions of the type e; no resumption

Constructors

Exc e

Instances

(MonadBase m m, SetMember (* -> *) (Lift *) (Lift * m) r, MonadBaseControl m (Eff r)) => MonadBaseControl m (Eff ((:) (* -> *) (Exc * e) r))

Associated Types

type StM (Eff (((* -> *) ': Exc * e) r) :: * -> *) a :: *

Methods

liftBaseWith :: (RunInBase (Eff (((* -> *) ': Exc * e) r)) m -> m a) -> Eff (((* -> *) ': Exc * e) r) a

restoreM :: StM (Eff (((* -> *) ': Exc * e) r)) a -> Eff (((* -> *) ': Exc * e) r) a

type StM (Eff ((:) (* -> *) (Exc * e) r)) a

type StM (Eff ((:) (* -> *) (Exc * e) r)) a = StM (Eff r) (Either e a)

type Fail = Exc ()

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

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

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

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

Makes an effect fail, preventing future effects from happening.

runError :: 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.

catchError :: 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. The handler is allowed to rethrow the exception

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.

rethrowError :: 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 :: Member (Exc e) r => Either e a -> Eff r a

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

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.

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

liftMaybe in a lifted Monad

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.