Safe Haskell	None
Language	Haskell2010

Control.Effect.Fail

Synopsis

newtype Fail (m :: * -> *) k = Fail String
class Monad m => MonadFail (m :: Type -> Type) where
- fail :: String -> m a
runFail :: FailC m a -> m (Either String a)
newtype FailC m a = FailC {
- runFailC :: ErrorC String m a
}

Documentation

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

Constructors

Fail String

Instances

Effect Fail Source #
Instance details Defined in Control.Effect.Fail Methods handle :: Functor f => f () -> (forall x. f (m x) -> n (f x)) -> Fail m (m a) -> Fail n (n (f a)) Source #
HFunctor Fail Source #
Instance details Defined in Control.Effect.Fail Methods fmap' :: (a -> b) -> Fail m a -> Fail m b Source # hmap :: (forall x. m x -> n x) -> Fail m a -> Fail n a Source #
Functor (Fail m) Source #
Instance details Defined in Control.Effect.Fail 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) Source #
Instance details Defined in Control.Effect.Fail Methods eff :: (Fail :+: sig) (FailC m) (FailC m a) -> FailC m a Source # ret :: a -> FailC m a Source #

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
Instance details Defined in Control.Monad.Fail Methods fail :: String -> [a] #
MonadFail Maybe	Since: base-4.9.0.0
Instance details Defined in Control.Monad.Fail Methods fail :: String -> Maybe a #
MonadFail IO	Since: base-4.9.0.0
Instance details Defined in Control.Monad.Fail Methods fail :: String -> IO a #
MonadFail ReadP	Since: base-4.9.0.0
Instance details Defined in Text.ParserCombinators.ReadP Methods fail :: String -> ReadP a #
MonadFail P	Since: base-4.9.0.0
Instance details Defined in Text.ParserCombinators.ReadP Methods fail :: String -> P a #
MonadFail m => MonadFail (ResourceC m) Source #
Instance details Defined in Control.Effect.Resource Methods fail :: String -> ResourceC m a #
MonadFail m => MonadFail (NonDetC m) Source #
Instance details Defined in Control.Effect.NonDet Methods fail :: String -> NonDetC m a #
MonadFail m => MonadFail (LiftC m) Source #
Instance details Defined in Control.Effect.Lift Methods fail :: String -> LiftC m a #
MonadFail m => MonadFail (FreshC m) Source #
Instance details Defined in Control.Effect.Fresh Methods fail :: String -> FreshC m a #
(Carrier sig m, Effect sig) => MonadFail (FailC m) Source #
Instance details Defined in Control.Effect.Fail Methods fail :: String -> FailC m a #
MonadFail m => MonadFail (CutC m) Source #
Instance details Defined in Control.Effect.Cut Methods fail :: String -> CutC m a #
MonadFail m => MonadFail (OnceC m) Source #
Instance details Defined in Control.Effect.Cull Methods fail :: String -> OnceC m a #
MonadFail m => MonadFail (CullC m) Source #
Instance details Defined in Control.Effect.Cull Methods fail :: String -> CullC m a #
MonadFail m => MonadFail (TraceByReturningC m) Source #
Instance details Defined in Control.Effect.Trace Methods fail :: String -> TraceByReturningC m a #
MonadFail m => MonadFail (TraceByIgnoringC m) Source #
Instance details Defined in Control.Effect.Trace Methods fail :: String -> TraceByIgnoringC m a #
MonadFail m => MonadFail (TraceByPrintingC m) Source #
Instance details Defined in Control.Effect.Trace Methods fail :: String -> TraceByPrintingC m a #
MonadFail f => MonadFail (Ap f)	Since: base-4.12.0.0
Instance details Defined in Data.Monoid Methods fail :: String -> Ap f a #
(Monad m, Error e) => MonadFail (ErrorT e m)
Instance details Defined in Control.Monad.Trans.Error Methods fail :: String -> ErrorT e m a #
MonadFail m => MonadFail (StateC s m) Source #
Instance details Defined in Control.Effect.State.Strict Methods fail :: String -> StateC s m a #
MonadFail m => MonadFail (StateC s m) Source #
Instance details Defined in Control.Effect.State.Lazy Methods fail :: String -> StateC s m a #
MonadFail m => MonadFail (ReaderC r m) Source #
Instance details Defined in Control.Effect.Reader Methods fail :: String -> ReaderC r m a #
MonadFail m => MonadFail (RandomC g m) Source #
Instance details Defined in Control.Effect.Random Methods fail :: String -> RandomC g m a #
MonadFail m => MonadFail (ErrorC e m) Source #
Instance details Defined in Control.Effect.Error Methods fail :: String -> ErrorC e m a #
MonadFail m => MonadFail (ResumableWithC err m) Source #
Instance details Defined in Control.Effect.Resumable Methods fail :: String -> ResumableWithC err m a #
MonadFail m => MonadFail (ResumableC err m) Source #
Instance details Defined in Control.Effect.Resumable Methods fail :: String -> ResumableC err m a #
MonadFail m => MonadFail (WriterC w m) Source #
Instance details Defined in Control.Effect.Writer Methods fail :: String -> WriterC w m a #

runFail :: FailC m a -> m (Either String a) Source #

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 Source #

Constructors

FailC
Fields runFailC :: ErrorC String m a

Instances

MonadTrans FailC Source #
Instance details Defined in Control.Effect.Fail Methods lift :: Monad m => m a -> FailC m a #
Monad m => Monad (FailC m) Source #
Instance details Defined in Control.Effect.Fail Methods (>>=) :: FailC m a -> (a -> FailC m b) -> FailC m b # (>>) :: FailC m a -> FailC m b -> FailC m b # return :: a -> FailC m a # fail :: String -> FailC m a #
Functor m => Functor (FailC m) Source #
Instance details Defined in Control.Effect.Fail Methods fmap :: (a -> b) -> FailC m a -> FailC m b # (<$) :: a -> FailC m b -> FailC m a #
(Carrier sig m, Effect sig) => MonadFail (FailC m) Source #
Instance details Defined in Control.Effect.Fail Methods fail :: String -> FailC m a #
Applicative m => Applicative (FailC m) Source #
Instance details Defined in Control.Effect.Fail Methods pure :: a -> FailC m a # (<>) :: FailC m (a -> b) -> FailC m a -> FailC m b # liftA2 :: (a -> b -> c) -> FailC m a -> FailC m b -> FailC m c # (>) :: FailC m a -> FailC m b -> FailC m b # (<*) :: FailC m a -> FailC m b -> FailC m a #
MonadIO m => MonadIO (FailC m) Source #
Instance details Defined in Control.Effect.Fail Methods liftIO :: IO a -> FailC m a #
Alternative m => Alternative (FailC m) Source #
Instance details Defined in Control.Effect.Fail Methods empty :: FailC m a # (<\|>) :: FailC m a -> FailC m a -> FailC m a # some :: FailC m a -> FailC m [a] # many :: FailC m a -> FailC m [a] #
(Alternative m, Monad m) => MonadPlus (FailC m) Source #
Instance details Defined in Control.Effect.Fail Methods mzero :: FailC m a # mplus :: FailC m a -> FailC m a -> FailC m a #
(Carrier sig m, Effect sig) => Carrier (Fail :+: sig) (FailC m) Source #
Instance details Defined in Control.Effect.Fail Methods eff :: (Fail :+: sig) (FailC m) (FailC m a) -> FailC m a Source # ret :: a -> FailC m a Source #