planet-mitchell-0.1.0: Planet Mitchell

Safe HaskellSafe
LanguageHaskell2010

Monad.Fail

Synopsis

Documentation

class Monad m => MonadFail (m :: * -> *) 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

Minimal complete definition

fail

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 Q 
Instance details

Defined in Language.Haskell.TH.Syntax

Methods

fail :: String -> Q a #

MonadFail IResult 
Instance details

Defined in Data.Aeson.Types.Internal

Methods

fail :: String -> IResult a #

MonadFail Result 
Instance details

Defined in Data.Aeson.Types.Internal

Methods

fail :: String -> Result a #

MonadFail Parser 
Instance details

Defined in Data.Aeson.Types.Internal

Methods

fail :: String -> Parser a #

MonadFail ReadPrec

Since: base-4.9.0.0

Instance details

Defined in Text.ParserCombinators.ReadPrec

Methods

fail :: String -> ReadPrec a #

MonadFail ReadP

Since: base-4.9.0.0

Instance details

Defined in Text.ParserCombinators.ReadP

Methods

fail :: String -> ReadP a #

MonadFail ReadM 
Instance details

Defined in Options.Applicative.Types

Methods

fail :: String -> ReadM a #

MonadFail P

Since: base-4.9.0.0

Instance details

Defined in Text.ParserCombinators.ReadP

Methods

fail :: String -> P a #

MonadFail (ST s)

Since: base-4.11.0.0

Instance details

Defined in GHC.ST

Methods

fail :: String -> ST s a #

Monad m => MonadFail (MaybeT m) 
Instance details

Defined in Control.Monad.Trans.Maybe

Methods

fail :: String -> MaybeT m a #

Monad m => MonadFail (ListT m) 
Instance details

Defined in List.Transformer

Methods

fail :: String -> ListT m a #

MonadFail m => MonadFail (IdentityT m) 
Instance details

Defined in Control.Monad.Trans.Identity

Methods

fail :: String -> IdentityT m a #

MonadFail m => MonadFail (ExceptT e m) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

fail :: String -> ExceptT e m a #

(Functor f, Monad m) => MonadFail (FreeT f m) 
Instance details

Defined in Control.Monad.Trans.Free

Methods

fail :: String -> FreeT f m 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 (StateT s m) 
Instance details

Defined in Control.Monad.Trans.State.Lazy

Methods

fail :: String -> StateT s m a #

MonadFail m => MonadFail (StateT s m) 
Instance details

Defined in Control.Monad.Trans.State.Strict

Methods

fail :: String -> StateT s m a #

MonadFail m => MonadFail (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.CPS.Internal

Methods

fail :: String -> WriterT w m a #

MonadFail m => MonadFail (ReaderT r m) 
Instance details

Defined in Control.Monad.Trans.Reader

Methods

fail :: String -> ReaderT r m a #

Stream s => MonadFail (ParsecT e s m) 
Instance details

Defined in Text.Megaparsec.Internal

Methods

fail :: String -> ParsecT e s m a #

MonadFail m => MonadFail (ContT r m) 
Instance details

Defined in Control.Monad.Trans.Cont

Methods

fail :: String -> ContT r m a #