Control.Effect.Fail

Documentation

newtype Fail (m :: * -> *) k

Constructors

Fail String

Instances

Effect Fail

Defined in Control.Effect.Fail.Internal

Methods

handle :: Functor f => f () -> (forall x. f (m x) -> n (f x)) -> Fail m (m a) -> Fail n (n (f a))

HFunctor Fail

Defined in Control.Effect.Fail.Internal

Methods

fmap' :: (a -> b) -> Fail m a -> Fail m b

hmap :: (forall x. m x -> n x) -> Fail m a -> Fail n a

Functor (Fail m)

Defined in Control.Effect.Fail.Internal

Methods

fmap :: (a -> b) -> Fail m a -> Fail m b

(<$) :: a -> Fail m b -> Fail m a

(Carrier sig m, Effect sig) => Carrier (Fail :+: sig) (FailC m)

Defined in Control.Effect.Fail

Methods

ret :: a -> FailC m a

eff :: (Fail :+: sig) (FailC m) (FailC m a) -> FailC m a

class Monad m => MonadFail (m :: Type -> Type) where

When a value is bound in do-notation, the pattern on the left hand side of <- might not match. In this case, this class provides a function to recover.

A Monad without a MonadFail instance may only be used in conjunction with pattern that always match, such as newtypes, tuples, data types with only a single data constructor, and irrefutable patterns (~pat).

Instances of MonadFail should satisfy the following law: fail s should be a left zero for >>=,

fail s >>= f  =  fail s

If your Monad is also MonadPlus, a popular definition is

fail _ = mzero

Since: base-4.9.0.0

Methods

fail :: String -> m a

Instances

MonadFail []

Since: base-4.9.0.0

Defined in Control.Monad.Fail

Methods

fail :: String -> [a]

MonadFail Maybe

Since: base-4.9.0.0

Defined in Control.Monad.Fail

Methods

fail :: String -> Maybe a

MonadFail IO

Since: base-4.9.0.0

Defined in Control.Monad.Fail

Methods

fail :: String -> IO a

MonadFail ReadP

Since: base-4.9.0.0

Defined in Text.ParserCombinators.ReadP

Methods

fail :: String -> ReadP a

MonadFail P

Since: base-4.9.0.0

Defined in Text.ParserCombinators.ReadP

Methods

fail :: String -> P a

(Member Fail sig, Carrier sig carrier) => MonadFail (Eff carrier)

Defined in Control.Effect.Internal

Methods

fail :: String -> Eff carrier a

MonadFail f => MonadFail (Ap f)

Since: base-4.12.0.0

Defined in Data.Monoid

Methods

fail :: String -> Ap f a

(Monad m, Error e) => MonadFail (ErrorT e m)

Defined in Control.Monad.Trans.Error

Methods

fail :: String -> ErrorT e m a

runFail :: (Carrier sig m, Effect sig) => Eff (FailC m) a -> m (Either String a)

Run a Fail effect, returning failure messages in Left and successful computations’ results in Right.

run (runFail (pure a)) == Right a

newtype FailC m a

Constructors

FailC

Fields

• runFailC :: m (Either String a)

Instances

(Carrier sig m, Effect sig) => Carrier (Fail :+: sig) (FailC m)

Defined in Control.Effect.Fail

Methods

ret :: a -> FailC m a

eff :: (Fail :+: sig) (FailC m) (FailC m a) -> FailC m a