Distribution.Compat.MonadFail

Compatibility layer for Control.Monad.Fail

Documentation

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 ReadPrec

Since: base-4.9.0.0

Defined in Text.ParserCombinators.ReadPrec

Methods

fail :: String -> ReadPrec a

MonadFail ReadP

Since: base-4.9.0.0

Defined in Text.ParserCombinators.ReadP

Methods

fail :: String -> ReadP a

MonadFail Get

Defined in Data.Binary.Get.Internal

Methods

fail :: String -> Get a

MonadFail P

Since: base-4.9.0.0

Defined in Text.ParserCombinators.ReadP

Methods

fail :: String -> P a

MonadFail ParsecParser

Defined in Distribution.Parsec

Methods

fail :: String -> ParsecParser a

Monad m => MonadFail (ListT m)

Defined in Control.Monad.Trans.List

Methods

fail :: String -> ListT m a

Monad m => MonadFail (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

fail :: String -> MaybeT m a

MonadFail f => MonadFail (Ap f)

Since: base-4.12.0.0

Defined in Data.Monoid

Methods

fail :: String -> Ap f a

MonadFail m => MonadFail (IdentityT m)

Defined in Control.Monad.Trans.Identity

Methods

fail :: String -> IdentityT m a

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

Defined in Control.Monad.Trans.Error

Methods

fail :: String -> ErrorT e m a

MonadFail m => MonadFail (ExceptT e m)

Defined in Control.Monad.Trans.Except

Methods

fail :: String -> ExceptT e m a

MonadFail m => MonadFail (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

fail :: String -> ReaderT r m a

MonadFail m => MonadFail (StateT s m)

Defined in Control.Monad.Trans.State.Lazy

Methods

fail :: String -> StateT s m a

MonadFail m => MonadFail (StateT s m)

Defined in Control.Monad.Trans.State.Strict

Methods

fail :: String -> StateT s m a

(Monoid w, MonadFail m) => MonadFail (WriterT w m)

Defined in Control.Monad.Trans.Writer.Lazy

Methods

fail :: String -> WriterT w m a

(Monoid w, MonadFail m) => MonadFail (WriterT w m)

Defined in Control.Monad.Trans.Writer.Strict

Methods

fail :: String -> WriterT w m a

MonadFail m => MonadFail (ContT r m)

Defined in Control.Monad.Trans.Cont

Methods

fail :: String -> ContT r m a

MonadFail (ParsecT s u m)

Since: parsec-3.1.12.0

Defined in Text.Parsec.Prim

Methods

fail :: String -> ParsecT s u m a

(Monoid w, MonadFail m) => MonadFail (RWST r w s m)

Defined in Control.Monad.Trans.RWS.Lazy

Methods

fail :: String -> RWST r w s m a

(Monoid w, MonadFail m) => MonadFail (RWST r w s m)

Defined in Control.Monad.Trans.RWS.Strict

Methods

fail :: String -> RWST r w s m a