Control.Monad.Levels.Except

Computations which may fail or throw exceptions.

Documentation

throwError :: forall e m a. HasError e m => e -> m a

Begin exception processing.

catchError :: forall e m a. HasError e m => m a -> (e -> m a) -> m a

Handle exception processing.

newtype ExceptT e m a :: * -> (* -> *) -> * -> *

A monad transformer that adds exceptions to other monads.

ExceptT constructs a monad parameterized over two things:

• e - The exception type.
• m - The inner monad.

The return function yields a computation that produces the given value, while >>= sequences two subcomputations, exiting on the first exception.

Constructors

ExceptT (m (Either e a))

Instances

MonadTower m => IsError e (ExceptT e m)

MonadTrans (ExceptT e)

MonadLevel m => ConstraintPassThrough (IsTransformer (ExceptT e)) (ListT m) True

(Functor m, Monad m, Monoid e) => Alternative (ExceptT e m)

Monad m => Monad (ExceptT e m)

Functor m => Functor (ExceptT e m)

MonadFix m => MonadFix (ExceptT e m)

(Monad m, Monoid e) => MonadPlus (ExceptT e m)

(Functor m, Monad m) => Applicative (ExceptT e m)

Foldable f => Foldable (ExceptT e f)

Traversable f => Traversable (ExceptT e f)

(Eq e, Eq1 m) => Eq1 (ExceptT e m)

(Ord e, Ord1 m) => Ord1 (ExceptT e m)

(Read e, Read1 m) => Read1 (ExceptT e m)

(Show e, Show1 m) => Show1 (ExceptT e m)

MonadIO m => MonadIO (ExceptT e m)

MonadTower m => MonadLevel_ (ExceptT e m)

MonadTower m => MonadTower_ (ExceptT e m)

(Eq e, Eq1 m, Eq a) => Eq (ExceptT e m a)

(Ord e, Ord1 m, Ord a) => Ord (ExceptT e m a)

(Read e, Read1 m, Read a) => Read (ExceptT e m a)

(Show e, Show1 m, Show a) => Show (ExceptT e m a)

type LowerMonad (ExceptT e m) = m

type WithLower_ (ExceptT e m) = AddIG

type AllowOtherValues (ExceptT e m) = True

type DefaultAllowConstraints (ExceptT e m) = True

type BaseMonad (ExceptT e m) = BaseMonad m

type InnerValue (ExceptT e m) a = Either e a

type HasError e m = SatisfyConstraint (IsError e) m

A monad stack that can throw and handle exceptions of type e.

class MonadTower m => IsError e m

Constraint for monads that can throw and handle exceptions.

Instances

IsError IOException IO

IsError e (Either e)

MonadTower m => IsError e (ExceptT e m)

ValidConstraint (IsError e)

MonadTower m => ConstraintPassThrough (IsError e) (ListT m) True

type ConstraintSatisfied (IsError e) m