Monad

Monad

class Applicative m => Monad (m :: * -> *) where

The Monad class defines the basic operations over a monad, a concept from a branch of mathematics known as category theory. From the perspective of a Haskell programmer, however, it is best to think of a monad as an abstract datatype of actions. Haskell's do expressions provide a convenient syntax for writing monadic expressions.

Instances of Monad should satisfy the following laws:

• return a >>= k  =  k a

• m >>= return  =  m

• m >>= (\x -> k x >>= h)  =  (m >>= k) >>= h

Furthermore, the Monad and Applicative operations should relate as follows:

• pure = return

• (<*>) = ap

The above laws imply:

• fmap f xs  =  xs >>= return . f

• (>>) = (*>)

and that pure and (<*>) satisfy the applicative functor laws.

The instances of Monad for lists, Maybe and IO defined in the Prelude satisfy these laws.

Minimal complete definition

(>>=)

Methods

(>>=) :: m a -> (a -> m b) -> m b infixl 1

Sequentially compose two actions, passing any value produced by the first as an argument to the second.

return :: a -> m a

Inject a value into the monadic type.

Instances

Monad []

Since: base-2.1

Defined in GHC.Base

Methods

(>>=) :: [a] -> (a -> [b]) -> [b]

(>>) :: [a] -> [b] -> [b]

return :: a -> [a]

fail :: String -> [a]

Monad Maybe

Since: base-2.1

Defined in GHC.Base

Methods

(>>=) :: Maybe a -> (a -> Maybe b) -> Maybe b

(>>) :: Maybe a -> Maybe b -> Maybe b

return :: a -> Maybe a

fail :: String -> Maybe a

Monad IO

Since: base-2.1

Defined in GHC.Base

Methods

(>>=) :: IO a -> (a -> IO b) -> IO b

(>>) :: IO a -> IO b -> IO b

return :: a -> IO a

fail :: String -> IO a

Monad Par1

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

(>>=) :: Par1 a -> (a -> Par1 b) -> Par1 b

(>>) :: Par1 a -> Par1 b -> Par1 b

return :: a -> Par1 a

fail :: String -> Par1 a

Monad Q

Defined in Language.Haskell.TH.Syntax

Methods

(>>=) :: Q a -> (a -> Q b) -> Q b

(>>) :: Q a -> Q b -> Q b

return :: a -> Q a

fail :: String -> Q a

Monad IResult

Defined in Data.Aeson.Types.Internal

Methods

(>>=) :: IResult a -> (a -> IResult b) -> IResult b

(>>) :: IResult a -> IResult b -> IResult b

return :: a -> IResult a

fail :: String -> IResult a

Monad Result

Defined in Data.Aeson.Types.Internal

Methods

(>>=) :: Result a -> (a -> Result b) -> Result b

(>>) :: Result a -> Result b -> Result b

return :: a -> Result a

fail :: String -> Result a

Monad Parser

Defined in Data.Aeson.Types.Internal

Methods

(>>=) :: Parser a -> (a -> Parser b) -> Parser b

(>>) :: Parser a -> Parser b -> Parser b

return :: a -> Parser a

fail :: String -> Parser a

Monad Complex

Since: base-4.9.0.0

Defined in Data.Complex

Methods

(>>=) :: Complex a -> (a -> Complex b) -> Complex b

(>>) :: Complex a -> Complex b -> Complex b

return :: a -> Complex a

fail :: String -> Complex a

Monad Min

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

(>>=) :: Min a -> (a -> Min b) -> Min b

(>>) :: Min a -> Min b -> Min b

return :: a -> Min a

fail :: String -> Min a

Monad Max

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

(>>=) :: Max a -> (a -> Max b) -> Max b

(>>) :: Max a -> Max b -> Max b

return :: a -> Max a

fail :: String -> Max a

Monad First

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

(>>=) :: First a -> (a -> First b) -> First b

(>>) :: First a -> First b -> First b

return :: a -> First a

fail :: String -> First a

Monad Last

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

(>>=) :: Last a -> (a -> Last b) -> Last b

(>>) :: Last a -> Last b -> Last b

return :: a -> Last a

fail :: String -> Last a

Monad Option

Since: base-4.9.0.0

Defined in Data.Semigroup

Methods

(>>=) :: Option a -> (a -> Option b) -> Option b

(>>) :: Option a -> Option b -> Option b

return :: a -> Option a

fail :: String -> Option a

Monad Identity

Since: base-4.8.0.0

Defined in Data.Functor.Identity

Methods

(>>=) :: Identity a -> (a -> Identity b) -> Identity b

(>>) :: Identity a -> Identity b -> Identity b

return :: a -> Identity a

fail :: String -> Identity a

Monad STM

Since: base-4.3.0.0

Defined in GHC.Conc.Sync

Methods

(>>=) :: STM a -> (a -> STM b) -> STM b

(>>) :: STM a -> STM b -> STM b

return :: a -> STM a

fail :: String -> STM a

Monad First

Defined in Data.Monoid

Methods

(>>=) :: First a -> (a -> First b) -> First b

(>>) :: First a -> First b -> First b

return :: a -> First a

fail :: String -> First a

Monad Last

Defined in Data.Monoid

Methods

(>>=) :: Last a -> (a -> Last b) -> Last b

(>>) :: Last a -> Last b -> Last b

return :: a -> Last a

fail :: String -> Last a

Monad Dual

Since: base-4.8.0.0

Defined in Data.Semigroup.Internal

Methods

(>>=) :: Dual a -> (a -> Dual b) -> Dual b

(>>) :: Dual a -> Dual b -> Dual b

return :: a -> Dual a

fail :: String -> Dual a

Monad Sum

Since: base-4.8.0.0

Defined in Data.Semigroup.Internal

Methods

(>>=) :: Sum a -> (a -> Sum b) -> Sum b

(>>) :: Sum a -> Sum b -> Sum b

return :: a -> Sum a

fail :: String -> Sum a

Monad Product

Since: base-4.8.0.0

Defined in Data.Semigroup.Internal

Methods

(>>=) :: Product a -> (a -> Product b) -> Product b

(>>) :: Product a -> Product b -> Product b

return :: a -> Product a

fail :: String -> Product a

Monad Down

Since: base-4.11.0.0

Defined in Data.Ord

Methods

(>>=) :: Down a -> (a -> Down b) -> Down b

(>>) :: Down a -> Down b -> Down b

return :: a -> Down a

fail :: String -> Down a

Monad ReadPrec

Since: base-2.1

Defined in Text.ParserCombinators.ReadPrec

Methods

(>>=) :: ReadPrec a -> (a -> ReadPrec b) -> ReadPrec b

(>>) :: ReadPrec a -> ReadPrec b -> ReadPrec b

return :: a -> ReadPrec a

fail :: String -> ReadPrec a

Monad ReadP

Since: base-2.1

Defined in Text.ParserCombinators.ReadP

Methods

(>>=) :: ReadP a -> (a -> ReadP b) -> ReadP b

(>>) :: ReadP a -> ReadP b -> ReadP b

return :: a -> ReadP a

fail :: String -> ReadP a

Monad NonEmpty

Since: base-4.9.0.0

Defined in GHC.Base

Methods

(>>=) :: NonEmpty a -> (a -> NonEmpty b) -> NonEmpty b

(>>) :: NonEmpty a -> NonEmpty b -> NonEmpty b

return :: a -> NonEmpty a

fail :: String -> NonEmpty a

Monad Put

Defined in Data.ByteString.Builder.Internal

Methods

(>>=) :: Put a -> (a -> Put b) -> Put b

(>>) :: Put a -> Put b -> Put b

return :: a -> Put a

fail :: String -> Put a

Monad Tree

Defined in Data.Tree

Methods

(>>=) :: Tree a -> (a -> Tree b) -> Tree b

(>>) :: Tree a -> Tree b -> Tree b

return :: a -> Tree a

fail :: String -> Tree a

Monad Seq

Defined in Data.Sequence.Internal

Methods

(>>=) :: Seq a -> (a -> Seq b) -> Seq b

(>>) :: Seq a -> Seq b -> Seq b

return :: a -> Seq a

fail :: String -> Seq a

Monad DList

Defined in Data.DList

Methods

(>>=) :: DList a -> (a -> DList b) -> DList b

(>>) :: DList a -> DList b -> DList b

return :: a -> DList a

fail :: String -> DList a

Monad Eval

Defined in Control.Parallel.Strategies

Methods

(>>=) :: Eval a -> (a -> Eval b) -> Eval b

(>>) :: Eval a -> Eval b -> Eval b

return :: a -> Eval a

fail :: String -> Eval a

Monad Vector

Defined in Data.Vector

Methods

(>>=) :: Vector a -> (a -> Vector b) -> Vector b

(>>) :: Vector a -> Vector b -> Vector b

return :: a -> Vector a

fail :: String -> Vector a

Monad Log

Defined in Numeric.Log

Methods

(>>=) :: Log a -> (a -> Log b) -> Log b

(>>) :: Log a -> Log b -> Log b

return :: a -> Log a

fail :: String -> Log a

Monad Managed

Defined in Control.Monad.Managed

Methods

(>>=) :: Managed a -> (a -> Managed b) -> Managed b

(>>) :: Managed a -> Managed b -> Managed b

return :: a -> Managed a

fail :: String -> Managed a

Monad ReadM

Defined in Options.Applicative.Types

Methods

(>>=) :: ReadM a -> (a -> ReadM b) -> ReadM b

(>>) :: ReadM a -> ReadM b -> ReadM b

return :: a -> ReadM a

fail :: String -> ReadM a

Monad ParserM

Defined in Options.Applicative.Types

Methods

(>>=) :: ParserM a -> (a -> ParserM b) -> ParserM b

(>>) :: ParserM a -> ParserM b -> ParserM b

return :: a -> ParserM a

fail :: String -> ParserM a

Monad ParserResult

Defined in Options.Applicative.Types

Methods

(>>=) :: ParserResult a -> (a -> ParserResult b) -> ParserResult b

(>>) :: ParserResult a -> ParserResult b -> ParserResult b

return :: a -> ParserResult a

fail :: String -> ParserResult a

Monad SmallArray

Defined in Data.Primitive.SmallArray

Methods

(>>=) :: SmallArray a -> (a -> SmallArray b) -> SmallArray b

(>>) :: SmallArray a -> SmallArray b -> SmallArray b

return :: a -> SmallArray a

fail :: String -> SmallArray a

Monad Array

Defined in Data.Primitive.Array

Methods

(>>=) :: Array a -> (a -> Array b) -> Array b

(>>) :: Array a -> Array b -> Array b

return :: a -> Array a

fail :: String -> Array a

Monad Future

Defined in Reactive.Banana.Types

Methods

(>>=) :: Future a -> (a -> Future b) -> Future b

(>>) :: Future a -> Future b -> Future b

return :: a -> Future a

fail :: String -> Future a

Monad Moment

Defined in Reactive.Banana.Types

Methods

(>>=) :: Moment a -> (a -> Moment b) -> Moment b

(>>) :: Moment a -> Moment b -> Moment b

return :: a -> Moment a

fail :: String -> Moment a

Monad MomentIO

Defined in Reactive.Banana.Types

Methods

(>>=) :: MomentIO a -> (a -> MomentIO b) -> MomentIO b

(>>) :: MomentIO a -> MomentIO b -> MomentIO b

return :: a -> MomentIO a

fail :: String -> MomentIO a

Monad Element

Defined in Control.Concurrent.Chan.Unagi.NoBlocking.Types

Methods

(>>=) :: Element a -> (a -> Element b) -> Element b

(>>) :: Element a -> Element b -> Element b

return :: a -> Element a

fail :: String -> Element a

Monad Memoized

Defined in UnliftIO.Memoize

Methods

(>>=) :: Memoized a -> (a -> Memoized b) -> Memoized b

(>>) :: Memoized a -> Memoized b -> Memoized b

return :: a -> Memoized a

fail :: String -> Memoized a

Monad P

Since: base-2.1

Defined in Text.ParserCombinators.ReadP

Methods

(>>=) :: P a -> (a -> P b) -> P b

(>>) :: P a -> P b -> P b

return :: a -> P a

fail :: String -> P a

() :=> (Monad ((->) a :: * -> *))

Defined in Data.Constraint

Methods

ins :: () :- Monad ((->) a)

() :=> (Monad [])

Defined in Data.Constraint

Methods

ins :: () :- Monad []

() :=> (Monad IO)

Defined in Data.Constraint

Methods

ins :: () :- Monad IO

() :=> (Monad (Either a))

Defined in Data.Constraint

Methods

ins :: () :- Monad (Either a)

() :=> (Monad Identity)

Defined in Data.Constraint

Methods

ins :: () :- Monad Identity

Monad (Either e)

Since: base-4.4.0.0

Defined in Data.Either

Methods

(>>=) :: Either e a -> (a -> Either e b) -> Either e b

(>>) :: Either e a -> Either e b -> Either e b

return :: a -> Either e a

fail :: String -> Either e a

Monad (U1 :: * -> *)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

(>>=) :: U1 a -> (a -> U1 b) -> U1 b

(>>) :: U1 a -> U1 b -> U1 b

return :: a -> U1 a

fail :: String -> U1 a

Monoid a => Monad ((,) a)

Since: base-4.9.0.0

Defined in GHC.Base

Methods

(>>=) :: (a, a0) -> (a0 -> (a, b)) -> (a, b)

(>>) :: (a, a0) -> (a, b) -> (a, b)

return :: a0 -> (a, a0)

fail :: String -> (a, a0)

Monad (ST s)

Since: base-2.1

Defined in GHC.ST

Methods

(>>=) :: ST s a -> (a -> ST s b) -> ST s b

(>>) :: ST s a -> ST s b -> ST s b

return :: a -> ST s a

fail :: String -> ST s a

Monad (Results s)

Defined in Text.Earley.Parser.Internal

Methods

(>>=) :: Results s a -> (a -> Results s b) -> Results s b

(>>) :: Results s a -> Results s b -> Results s b

return :: a -> Results s a

fail :: String -> Results s a

Monad (Grammar r)

Defined in Text.Earley.Grammar

Methods

(>>=) :: Grammar r a -> (a -> Grammar r b) -> Grammar r b

(>>) :: Grammar r a -> Grammar r b -> Grammar r b

return :: a -> Grammar r a

fail :: String -> Grammar r a

Representable f => Monad (Co f)

Defined in Data.Functor.Rep

Methods

(>>=) :: Co f a -> (a -> Co f b) -> Co f b

(>>) :: Co f a -> Co f b -> Co f b

return :: a -> Co f a

fail :: String -> Co f a

Monad m => Monad (WrappedMonad m)

Defined in Control.Applicative

Methods

(>>=) :: WrappedMonad m a -> (a -> WrappedMonad m b) -> WrappedMonad m b

(>>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b

return :: a -> WrappedMonad m a

fail :: String -> WrappedMonad m a

ArrowApply a => Monad (ArrowMonad a)

Since: base-2.1

Defined in Control.Arrow

Methods

(>>=) :: ArrowMonad a a0 -> (a0 -> ArrowMonad a b) -> ArrowMonad a b

(>>) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a b

return :: a0 -> ArrowMonad a a0

fail :: String -> ArrowMonad a a0

Monad (Proxy :: * -> *)

Since: base-4.7.0.0

Defined in Data.Proxy

Methods

(>>=) :: Proxy a -> (a -> Proxy b) -> Proxy b

(>>) :: Proxy a -> Proxy b -> Proxy b

return :: a -> Proxy a

fail :: String -> Proxy a

Monad m => Monad (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

(>>=) :: MaybeT m a -> (a -> MaybeT m b) -> MaybeT m b

(>>) :: MaybeT m a -> MaybeT m b -> MaybeT m b

return :: a -> MaybeT m a

fail :: String -> MaybeT m a

Alternative f => Monad (Cofree f)

Defined in Control.Comonad.Cofree

Methods

(>>=) :: Cofree f a -> (a -> Cofree f b) -> Cofree f b

(>>) :: Cofree f a -> Cofree f b -> Cofree f b

return :: a -> Cofree f a

fail :: String -> Cofree f a

Functor f => Monad (Free f)

Defined in Control.Monad.Free

Methods

(>>=) :: Free f a -> (a -> Free f b) -> Free f b

(>>) :: Free f a -> Free f b -> Free f b

return :: a -> Free f a

fail :: String -> Free f a

Monad m => Monad (Yoneda m)

Defined in Data.Functor.Yoneda

Methods

(>>=) :: Yoneda m a -> (a -> Yoneda m b) -> Yoneda m b

(>>) :: Yoneda m a -> Yoneda m b -> Yoneda m b

return :: a -> Yoneda m a

fail :: String -> Yoneda m a

Monad (ReifiedGetter s)

Defined in Control.Lens.Reified

Methods

(>>=) :: ReifiedGetter s a -> (a -> ReifiedGetter s b) -> ReifiedGetter s b

(>>) :: ReifiedGetter s a -> ReifiedGetter s b -> ReifiedGetter s b

return :: a -> ReifiedGetter s a

fail :: String -> ReifiedGetter s a

Monad (ReifiedFold s)

Defined in Control.Lens.Reified

Methods

(>>=) :: ReifiedFold s a -> (a -> ReifiedFold s b) -> ReifiedFold s b

(>>) :: ReifiedFold s a -> ReifiedFold s b -> ReifiedFold s b

return :: a -> ReifiedFold s a

fail :: String -> ReifiedFold s a

Monad m => Monad (ListT m)

Defined in List.Transformer

Methods

(>>=) :: ListT m a -> (a -> ListT m b) -> ListT m b

(>>) :: ListT m a -> ListT m b -> ListT m b

return :: a -> ListT m a

fail :: String -> ListT m a

Monad (LogicT m)

Defined in Control.Monad.Logic

Methods

(>>=) :: LogicT m a -> (a -> LogicT m b) -> LogicT m b

(>>) :: LogicT m a -> LogicT m b -> LogicT m b

return :: a -> LogicT m a

fail :: String -> LogicT m a

(Monad (Rep p), Representable p) => Monad (Prep p)

Defined in Data.Profunctor.Rep

Methods

(>>=) :: Prep p a -> (a -> Prep p b) -> Prep p b

(>>) :: Prep p a -> Prep p b -> Prep p b

return :: a -> Prep p a

fail :: String -> Prep p a

Monad (IParser t)

Defined in Data.Text.Internal.Read

Methods

(>>=) :: IParser t a -> (a -> IParser t b) -> IParser t b

(>>) :: IParser t a -> IParser t b -> IParser t b

return :: a -> IParser t a

fail :: String -> IParser t a

Monad (SetM s)

Defined in Data.Graph

Methods

(>>=) :: SetM s a -> (a -> SetM s b) -> SetM s b

(>>) :: SetM s a -> SetM s b -> SetM s b

return :: a -> SetM s a

fail :: String -> SetM s a

Monad (IncrementalDecoder s)

Defined in Codec.CBOR.Read

Methods

(>>=) :: IncrementalDecoder s a -> (a -> IncrementalDecoder s b) -> IncrementalDecoder s b

(>>) :: IncrementalDecoder s a -> IncrementalDecoder s b -> IncrementalDecoder s b

return :: a -> IncrementalDecoder s a

fail :: String -> IncrementalDecoder s a

Class (Applicative f) (Monad f)

Defined in Data.Constraint

Methods

cls :: Monad f :- Applicative f

(Monad m) :=> (Functor (WrappedMonad m))

Defined in Data.Constraint

Methods

ins :: Monad m :- Functor (WrappedMonad m)

(Monad m) :=> (Applicative (WrappedMonad m))

Defined in Data.Constraint

Methods

ins :: Monad m :- Applicative (WrappedMonad m)

Monad f => Monad (Rec1 f)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

(>>=) :: Rec1 f a -> (a -> Rec1 f b) -> Rec1 f b

(>>) :: Rec1 f a -> Rec1 f b -> Rec1 f b

return :: a -> Rec1 f a

fail :: String -> Rec1 f a

Monad (Results t s)

Defined in Text.Earley.Generator.Internal

Methods

(>>=) :: Results t s a -> (a -> Results t s b) -> Results t s b

(>>) :: Results t s a -> Results t s b -> Results t s b

return :: a -> Results t s a

fail :: String -> Results t s a

Monad f => Monad (Alt f)

Defined in Data.Semigroup.Internal

Methods

(>>=) :: Alt f a -> (a -> Alt f b) -> Alt f b

(>>) :: Alt f a -> Alt f b -> Alt f b

return :: a -> Alt f a

fail :: String -> Alt f a

Monad m => Monad (IdentityT m)

Defined in Control.Monad.Trans.Identity

Methods

(>>=) :: IdentityT m a -> (a -> IdentityT m b) -> IdentityT m b

(>>) :: IdentityT m a -> IdentityT m b -> IdentityT m b

return :: a -> IdentityT m a

fail :: String -> IdentityT m a

(Applicative f, Monad f) => Monad (WhenMissing f x)

Equivalent to ReaderT k (ReaderT x (MaybeT f)).

Since: containers-0.5.9

Defined in Data.IntMap.Internal

Methods

(>>=) :: WhenMissing f x a -> (a -> WhenMissing f x b) -> WhenMissing f x b

(>>) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x b

return :: a -> WhenMissing f x a

fail :: String -> WhenMissing f x a

Monad m => Monad (ExceptT e m)

Defined in Control.Monad.Trans.Except

Methods

(>>=) :: ExceptT e m a -> (a -> ExceptT e m b) -> ExceptT e m b

(>>) :: ExceptT e m a -> ExceptT e m b -> ExceptT e m b

return :: a -> ExceptT e m a

fail :: String -> ExceptT e m a

Monad m => Monad (GT m g)

Defined in Data.Graph.Inductive.Query.Monad

Methods

(>>=) :: GT m g a -> (a -> GT m g b) -> GT m g b

(>>) :: GT m g a -> GT m g b -> GT m g b

return :: a -> GT m g a

fail :: String -> GT m g a

(Functor f, Monad m) => Monad (FreeT f m)

Defined in Control.Monad.Trans.Free

Methods

(>>=) :: FreeT f m a -> (a -> FreeT f m b) -> FreeT f m b

(>>) :: FreeT f m a -> FreeT f m b -> FreeT f m b

return :: a -> FreeT f m a

fail :: String -> FreeT f m a

(Alternative f, Monad w) => Monad (CofreeT f w)

Defined in Control.Comonad.Trans.Cofree

Methods

(>>=) :: CofreeT f w a -> (a -> CofreeT f w b) -> CofreeT f w b

(>>) :: CofreeT f w a -> CofreeT f w b -> CofreeT f w b

return :: a -> CofreeT f w a

fail :: String -> CofreeT f w a

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

Defined in Control.Monad.Trans.Error

Methods

(>>=) :: ErrorT e m a -> (a -> ErrorT e m b) -> ErrorT e m b

(>>) :: ErrorT e m a -> ErrorT e m b -> ErrorT e m b

return :: a -> ErrorT e m a

fail :: String -> ErrorT e m a

Monad (Indexed i a)

Defined in Control.Lens.Internal.Indexed

Methods

(>>=) :: Indexed i a a0 -> (a0 -> Indexed i a b) -> Indexed i a b

(>>) :: Indexed i a a0 -> Indexed i a b -> Indexed i a b

return :: a0 -> Indexed i a a0

fail :: String -> Indexed i a a0

Monad m => Monad (StateT s m)

Defined in Control.Monad.Trans.State.Lazy

Methods

(>>=) :: StateT s m a -> (a -> StateT s m b) -> StateT s m b

(>>) :: StateT s m a -> StateT s m b -> StateT s m b

return :: a -> StateT s m a

fail :: String -> StateT s m a

Monad (STE e s)

Defined in Control.Monad.STE.Internal

Methods

(>>=) :: STE e s a -> (a -> STE e s b) -> STE e s b

(>>) :: STE e s a -> STE e s b -> STE e s b

return :: a -> STE e s a

fail :: String -> STE e s a

Monad m => Monad (StateT s m)

Defined in Control.Monad.Trans.State.Strict

Methods

(>>=) :: StateT s m a -> (a -> StateT s m b) -> StateT s m b

(>>) :: StateT s m a -> StateT s m b -> StateT s m b

return :: a -> StateT s m a

fail :: String -> StateT s m a

Monad f => Monad (Star f a)

Defined in Data.Profunctor.Types

Methods

(>>=) :: Star f a a0 -> (a0 -> Star f a b) -> Star f a b

(>>) :: Star f a a0 -> Star f a b -> Star f a b

return :: a0 -> Star f a a0

fail :: String -> Star f a a0

Monad (Costar f a)

Defined in Data.Profunctor.Types

Methods

(>>=) :: Costar f a a0 -> (a0 -> Costar f a b) -> Costar f a b

(>>) :: Costar f a a0 -> Costar f a b -> Costar f a b

return :: a0 -> Costar f a a0

fail :: String -> Costar f a a0

Monad (Tagged s)

Defined in Data.Tagged

Methods

(>>=) :: Tagged s a -> (a -> Tagged s b) -> Tagged s b

(>>) :: Tagged s a -> Tagged s b -> Tagged s b

return :: a -> Tagged s a

fail :: String -> Tagged s a

Monad m => Monad (WriterT w m)

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

Methods

(>>=) :: WriterT w m a -> (a -> WriterT w m b) -> WriterT w m b

(>>) :: WriterT w m a -> WriterT w m b -> WriterT w m b

return :: a -> WriterT w m a

fail :: String -> WriterT w m a

Class (Monad f, Alternative f) (MonadPlus f)

Defined in Data.Constraint

Methods

cls :: MonadPlus f :- (Monad f, Alternative f)

Monad ((->) r :: * -> *)

Since: base-2.1

Defined in GHC.Base

Methods

(>>=) :: (r -> a) -> (a -> r -> b) -> r -> b

(>>) :: (r -> a) -> (r -> b) -> r -> b

return :: a -> r -> a

fail :: String -> r -> a

(Monad f, Monad g) => Monad (f :*: g)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

(>>=) :: (f :*: g) a -> (a -> (f :*: g) b) -> (f :*: g) b

(>>) :: (f :*: g) a -> (f :*: g) b -> (f :*: g) b

return :: a -> (f :*: g) a

fail :: String -> (f :*: g) a

(Monad f, Monad g) => Monad (Product f g)

Since: base-4.9.0.0

Defined in Data.Functor.Product

Methods

(>>=) :: Product f g a -> (a -> Product f g b) -> Product f g b

(>>) :: Product f g a -> Product f g b -> Product f g b

return :: a -> Product f g a

fail :: String -> Product f g a

Monad (Cokleisli w a)

Defined in Control.Comonad

Methods

(>>=) :: Cokleisli w a a0 -> (a0 -> Cokleisli w a b) -> Cokleisli w a b

(>>) :: Cokleisli w a a0 -> Cokleisli w a b -> Cokleisli w a b

return :: a0 -> Cokleisli w a a0

fail :: String -> Cokleisli w a a0

(Monad f, Applicative f) => Monad (WhenMatched f x y)

Equivalent to ReaderT Key (ReaderT x (ReaderT y (MaybeT f)))

Since: containers-0.5.9

Defined in Data.IntMap.Internal

Methods

(>>=) :: WhenMatched f x y a -> (a -> WhenMatched f x y b) -> WhenMatched f x y b

(>>) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y b

return :: a -> WhenMatched f x y a

fail :: String -> WhenMatched f x y a

(Applicative f, Monad f) => Monad (WhenMissing f k x)

Equivalent to ReaderT k (ReaderT x (MaybeT f)) .

Since: containers-0.5.9

Defined in Data.Map.Internal

Methods

(>>=) :: WhenMissing f k x a -> (a -> WhenMissing f k x b) -> WhenMissing f k x b

(>>) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x b

return :: a -> WhenMissing f k x a

fail :: String -> WhenMissing f k x a

Monad m => Monad (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

(>>=) :: ReaderT r m a -> (a -> ReaderT r m b) -> ReaderT r m b

(>>) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m b

return :: a -> ReaderT r m a

fail :: String -> ReaderT r m a

Stream s => Monad (ParsecT e s m)

return returns a parser that succeeds without consuming input.

Defined in Text.Megaparsec.Internal

Methods

(>>=) :: ParsecT e s m a -> (a -> ParsecT e s m b) -> ParsecT e s m b

(>>) :: ParsecT e s m a -> ParsecT e s m b -> ParsecT e s m b

return :: a -> ParsecT e s m a

fail :: String -> ParsecT e s m a

Monad (ContT r m)

Defined in Control.Monad.Trans.Cont

Methods

(>>=) :: ContT r m a -> (a -> ContT r m b) -> ContT r m b

(>>) :: ContT r m a -> ContT r m b -> ContT r m b

return :: a -> ContT r m a

fail :: String -> ContT r m a

Monad f => Monad (M1 i c f)

Since: base-4.9.0.0

Defined in GHC.Generics

Methods

(>>=) :: M1 i c f a -> (a -> M1 i c f b) -> M1 i c f b

(>>) :: M1 i c f a -> M1 i c f b -> M1 i c f b

return :: a -> M1 i c f a

fail :: String -> M1 i c f a

(Monad f, Applicative f) => Monad (WhenMatched f k x y)

Equivalent to ReaderT k (ReaderT x (ReaderT y (MaybeT f)))

Since: containers-0.5.9

Defined in Data.Map.Internal

Methods

(>>=) :: WhenMatched f k x y a -> (a -> WhenMatched f k x y b) -> WhenMatched f k x y b

(>>) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y b

return :: a -> WhenMatched f k x y a

fail :: String -> WhenMatched f k x y a

(=<<) :: Monad m => (a -> m b) -> m a -> m b infixr 1

Same as >>=, but with the arguments interchanged.

(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c infixr 1

Left-to-right Kleisli composition of monads.

(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c infixr 1

Right-to-left Kleisli composition of monads. (>=>), with the arguments flipped.

Note how this operator resembles function composition (.):

(.)   ::            (b ->   c) -> (a ->   b) -> a ->   c
(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c

(<$!>) :: Monad m => (a -> b) -> m a -> m b infixl 4

Strict version of <$>.

Since: base-4.8.0.0

join :: Monad m => m (m a) -> m a

The join function is the conventional monad join operator. It is used to remove one level of monadic structure, projecting its bound argument into the outer level.

loopM :: Monad m => (a -> m (Either a b)) -> a -> m b

A monadic version of loop, where the predicate returns Left as a seed for the next loop or Right to abort the loop.

unlessM :: Monad m => m Bool -> m () -> m ()

Like unless, but where the test can be monadic.

whenJustM :: Monad m => m (Maybe a) -> (a -> m ()) -> m ()

Like whenJust, but where the test can be monadic.

whenM :: Monad m => m Bool -> m () -> m ()

Like when, but where the test can be monadic.

whileM :: Monad m => m Bool -> m ()

Keep running an operation until it becomes False. As an example:

whileM $ do sleep 0.1; notM $ doesFileExist "foo.txt"
readFile "foo.txt"

If you need some state persisted between each test, use loopM.

Newtypes

newtype Kleisli (m :: * -> *) a b

Kleisli arrows of a monad.

Constructors

Kleisli

Fields

• runKleisli :: a -> m b

Instances

Monad m => Arrow (Kleisli m)

Since: base-2.1

Defined in Control.Arrow

Methods

arr :: (b -> c) -> Kleisli m b c

first :: Kleisli m b c -> Kleisli m (b, d) (c, d)

second :: Kleisli m b c -> Kleisli m (d, b) (d, c)

(***) :: Kleisli m b c -> Kleisli m b' c' -> Kleisli m (b, b') (c, c')

(&&&) :: Kleisli m b c -> Kleisli m b c' -> Kleisli m b (c, c')

MonadPlus m => ArrowZero (Kleisli m)

Since: base-2.1

Defined in Control.Arrow

Methods

zeroArrow :: Kleisli m b c

MonadPlus m => ArrowPlus (Kleisli m)

Since: base-2.1

Defined in Control.Arrow

Methods

(<+>) :: Kleisli m b c -> Kleisli m b c -> Kleisli m b c

Monad m => ArrowChoice (Kleisli m)

Since: base-2.1

Defined in Control.Arrow

Methods

left :: Kleisli m b c -> Kleisli m (Either b d) (Either c d)

right :: Kleisli m b c -> Kleisli m (Either d b) (Either d c)

(+++) :: Kleisli m b c -> Kleisli m b' c' -> Kleisli m (Either b b') (Either c c')

(|||) :: Kleisli m b d -> Kleisli m c d -> Kleisli m (Either b c) d

Monad m => ArrowApply (Kleisli m)

Since: base-2.1

Defined in Control.Arrow

Methods

app :: Kleisli m (Kleisli m b c, b) c

MonadFix m => ArrowLoop (Kleisli m)

Beware that for many monads (those for which the >>= operation is strict) this instance will not satisfy the right-tightening law required by the ArrowLoop class.

Since: base-2.1

Defined in Control.Arrow

Methods

loop :: Kleisli m (b, d) (c, d) -> Kleisli m b c

Monad m => Profunctor (Kleisli m)

Defined in Data.Profunctor.Unsafe

Methods

dimap :: (a -> b) -> (c -> d) -> Kleisli m b c -> Kleisli m a d

lmap :: (a -> b) -> Kleisli m b c -> Kleisli m a c

rmap :: (b -> c) -> Kleisli m a b -> Kleisli m a c

(#.) :: Coercible c b => (b -> c) -> Kleisli m a b -> Kleisli m a c

(.#) :: Coercible b a => Kleisli m b c -> (a -> b) -> Kleisli m a c

(Monad m, Functor m) => Representable (Kleisli m)

Defined in Data.Profunctor.Rep

Associated Types

type Rep (Kleisli m) :: * -> *

Methods

tabulate :: (d -> Rep (Kleisli m) c) -> Kleisli m d c

Monad m => Choice (Kleisli m)

Defined in Data.Profunctor.Choice

Methods

left' :: Kleisli m a b -> Kleisli m (Either a c) (Either b c)

right' :: Kleisli m a b -> Kleisli m (Either c a) (Either c b)

(Monad m, Distributive m) => Mapping (Kleisli m)

Defined in Data.Profunctor.Mapping

Methods

map' :: Functor f => Kleisli m a b -> Kleisli m (f a) (f b)

(Distributive f, Monad f) => Closed (Kleisli f)

Defined in Data.Profunctor.Closed

Methods

closed :: Kleisli f a b -> Kleisli f (x -> a) (x -> b)

Monad m => Strong (Kleisli m)

Defined in Data.Profunctor.Strong

Methods

first' :: Kleisli m a b -> Kleisli m (a, c) (b, c)

second' :: Kleisli m a b -> Kleisli m (c, a) (c, b)

MonadFix m => Costrong (Kleisli m)

Defined in Data.Profunctor.Strong

Methods

unfirst :: Kleisli m (a, d) (b, d) -> Kleisli m a b

unsecond :: Kleisli m (d, a) (d, b) -> Kleisli m a b

Monad m => Category (Kleisli m :: * -> * -> *)

Since: base-3.0

Defined in Control.Arrow

Methods

id :: Kleisli m a a

(.) :: Kleisli m b c -> Kleisli m a b -> Kleisli m a c

Bind m => Semigroupoid (Kleisli m :: * -> * -> *)

Defined in Data.Semigroupoid

Methods

o :: Kleisli m j k1 -> Kleisli m i j -> Kleisli m i k1

Wrapped (Kleisli m a b)

Defined in Control.Lens.Wrapped

Associated Types

type Unwrapped (Kleisli m a b) :: *

Methods

_Wrapped' :: Iso' (Kleisli m a b) (Unwrapped (Kleisli m a b))

t ~ Kleisli m' a' b' => Rewrapped (Kleisli m a b) t

Defined in Control.Lens.Wrapped

type Rep (Kleisli m)

Defined in Data.Profunctor.Rep

type Rep (Kleisli m) = m

type Unwrapped (Kleisli m a b)

Defined in Control.Lens.Wrapped

type Unwrapped (Kleisli m a b) = a -> m b

MMonad

class (MFunctor t, MonadTrans t) => MMonad (t :: (* -> *) -> * -> *) where

A monad in the category of monads, using lift from MonadTrans as the analog of return and embed as the analog of (=<<):

embed lift = id

embed f (lift m) = f m

embed g (embed f t) = embed (\m -> embed g (f m)) t

Minimal complete definition

embed

Methods

embed :: Monad n => (forall a. m a -> t n a) -> t m b -> t n b

Embed a newly created MMonad layer within an existing layer

embed is analogous to (=<<)

Instances

MMonad MaybeT

Defined in Control.Monad.Morph

Methods

embed :: Monad n => (forall a. m a -> MaybeT n a) -> MaybeT m b -> MaybeT n b

MMonad ListT

Defined in Control.Monad.Morph

Methods

embed :: Monad n => (forall a. m a -> ListT n a) -> ListT m b -> ListT n b

MMonad (IdentityT :: (* -> *) -> * -> *)

Defined in Control.Monad.Morph

Methods

embed :: Monad n => (forall a. m a -> IdentityT n a) -> IdentityT m b -> IdentityT n b

MMonad (ExceptT e)

Defined in Control.Monad.Morph

Methods

embed :: Monad n => (forall a. m a -> ExceptT e n a) -> ExceptT e m b -> ExceptT e n b

Error e => MMonad (ErrorT e)

Defined in Control.Monad.Morph

Methods

embed :: Monad n => (forall a. m a -> ErrorT e n a) -> ErrorT e m b -> ErrorT e n b

Monoid w => MMonad (WriterT w)

Defined in Control.Monad.Morph

Methods

embed :: Monad n => (forall a. m a -> WriterT w n a) -> WriterT w m b -> WriterT w n b

Monoid w => MMonad (WriterT w)

Defined in Control.Monad.Morph

Methods

embed :: Monad n => (forall a. m a -> WriterT w n a) -> WriterT w m b -> WriterT w n b

MMonad (ReaderT r :: (* -> *) -> * -> *)

Defined in Control.Monad.Morph

Methods

embed :: Monad n => (forall a. m a -> ReaderT r n a) -> ReaderT r m b -> ReaderT r n b

squash :: (Monad m, MMonad t) => t (t m) a -> t m a

Squash two MMonad layers into a single layer

squash is analogous to join

(>|>) :: (Monad m3, MMonad t) => (forall a. m1 a -> t m2 a) -> (forall b. m2 b -> t m3 b) -> m1 c -> t m3 c infixr 2

Compose two MMonad layer-building functions

(>|>) is analogous to (>=>)

(<|<) :: (Monad m3, MMonad t) => (forall b. m2 b -> t m3 b) -> (forall a. m1 a -> t m2 a) -> m1 c -> t m3 c infixl 2

Equivalent to (>|>) with the arguments flipped

(<|<) is analogous to (<=<)

(=<|) :: (Monad n, MMonad t) => (forall a. m a -> t n a) -> t m b -> t n b infixr 2

An infix operator equivalent to embed

(=<|) is analogous to (=<<)

(|>=) :: (Monad n, MMonad t) => t m b -> (forall a. m a -> t n a) -> t n b infixl 2

Equivalent to (=<|) with the arguments flipped

(|>=) is analogous to (>>=)