Copyright	(c) The University of Glasgow 2001
License	BSD-style (see the file libraries/base/LICENSE)
Maintainer	libraries@haskell.org
Stability	provisional
Portability	portable
Safe Haskell	Safe
Language	Haskell2010

Control.Monad.Instances

Description

Deprecated: This module now contains no instances and will be removed in the future

This module is DEPRECATED and will be removed in the future!

Functor and Monad instances for (->) r and Functor instances for (,) a and Either a.

Synopsis

Documentation

class Functor f where #

The Functor class is used for types that can be mapped over. Instances of Functor should satisfy the following laws:

fmap id  ==  id
fmap (f . g)  ==  fmap f . fmap g

The instances of Functor for lists, Maybe and IO satisfy these laws.

Minimal complete definition

fmap

Methods

fmap :: (a -> b) -> f a -> f b #

(<$) :: a -> f b -> f a infixl 4 #

Replace all locations in the input with the same value. The default definition is fmap . const, but this may be overridden with a more efficient version.

Instances

Functor [] #	Since: 2.1
Methods fmap :: (a -> b) -> [a] -> [b] # (<$) :: a -> [b] -> [a] #
Functor Maybe #	Since: 2.1
Methods fmap :: (a -> b) -> Maybe a -> Maybe b # (<$) :: a -> Maybe b -> Maybe a #
Functor IO #	Since: 2.1
Methods fmap :: (a -> b) -> IO a -> IO b # (<$) :: a -> IO b -> IO a #
Functor Par1 #
Methods fmap :: (a -> b) -> Par1 a -> Par1 b # (<$) :: a -> Par1 b -> Par1 a #
Functor ReadP #	Since: 2.1
Methods fmap :: (a -> b) -> ReadP a -> ReadP b # (<$) :: a -> ReadP b -> ReadP a #
Functor ReadPrec #	Since: 2.1
Methods fmap :: (a -> b) -> ReadPrec a -> ReadPrec b # (<$) :: a -> ReadPrec b -> ReadPrec a #
Functor Last #
Methods fmap :: (a -> b) -> Last a -> Last b # (<$) :: a -> Last b -> Last a #
Functor First #
Methods fmap :: (a -> b) -> First a -> First b # (<$) :: a -> First b -> First a #
Functor Product #	Since: 4.8.0.0
Methods fmap :: (a -> b) -> Product a -> Product b # (<$) :: a -> Product b -> Product a #
Functor Sum #	Since: 4.8.0.0
Methods fmap :: (a -> b) -> Sum a -> Sum b # (<$) :: a -> Sum b -> Sum a #
Functor Dual #	Since: 4.8.0.0
Methods fmap :: (a -> b) -> Dual a -> Dual b # (<$) :: a -> Dual b -> Dual a #
Functor STM #	Since: 4.3.0.0
Methods fmap :: (a -> b) -> STM a -> STM b # (<$) :: a -> STM b -> STM a #
Functor Handler #	Since: 4.6.0.0
Methods fmap :: (a -> b) -> Handler a -> Handler b # (<$) :: a -> Handler b -> Handler a #
Functor Identity #	Since: 4.8.0.0
Methods fmap :: (a -> b) -> Identity a -> Identity b # (<$) :: a -> Identity b -> Identity a #
Functor ZipList #
Methods fmap :: (a -> b) -> ZipList a -> ZipList b # (<$) :: a -> ZipList b -> ZipList a #
Functor ArgDescr #	Since: 4.6.0.0
Methods fmap :: (a -> b) -> ArgDescr a -> ArgDescr b # (<$) :: a -> ArgDescr b -> ArgDescr a #
Functor OptDescr #	Since: 4.6.0.0
Methods fmap :: (a -> b) -> OptDescr a -> OptDescr b # (<$) :: a -> OptDescr b -> OptDescr a #
Functor ArgOrder #	Since: 4.6.0.0
Methods fmap :: (a -> b) -> ArgOrder a -> ArgOrder b # (<$) :: a -> ArgOrder b -> ArgOrder a #
Functor NonEmpty #	Since: 4.9.0.0
Methods fmap :: (a -> b) -> NonEmpty a -> NonEmpty b # (<$) :: a -> NonEmpty b -> NonEmpty a #
Functor Option #	Since: 4.9.0.0
Methods fmap :: (a -> b) -> Option a -> Option b # (<$) :: a -> Option b -> Option a #
Functor Last #	Since: 4.9.0.0
Methods fmap :: (a -> b) -> Last a -> Last b # (<$) :: a -> Last b -> Last a #
Functor First #	Since: 4.9.0.0
Methods fmap :: (a -> b) -> First a -> First b # (<$) :: a -> First b -> First a #
Functor Max #	Since: 4.9.0.0
Methods fmap :: (a -> b) -> Max a -> Max b # (<$) :: a -> Max b -> Max a #
Functor Min #	Since: 4.9.0.0
Methods fmap :: (a -> b) -> Min a -> Min b # (<$) :: a -> Min b -> Min a #
Functor Complex #
Methods fmap :: (a -> b) -> Complex a -> Complex b # (<$) :: a -> Complex b -> Complex a #
Functor (Either a) #	Since: 3.0
Methods fmap :: (a -> b) -> Either a a -> Either a b # (<$) :: a -> Either a b -> Either a a #
Functor (V1 *) #
Methods fmap :: (a -> b) -> V1 * a -> V1 * b # (<$) :: a -> V1 * b -> V1 * a #
Functor (U1 *) #	Since: 4.9.0.0
Methods fmap :: (a -> b) -> U1 * a -> U1 * b # (<$) :: a -> U1 * b -> U1 * a #
Functor ((,) a) #	Since: 2.1
Methods fmap :: (a -> b) -> (a, a) -> (a, b) # (<$) :: a -> (a, b) -> (a, a) #
Functor (ST s) #	Since: 2.1
Methods fmap :: (a -> b) -> ST s a -> ST s b # (<$) :: a -> ST s b -> ST s a #
Functor (Proxy *) #	Since: 4.7.0.0
Methods fmap :: (a -> b) -> Proxy * a -> Proxy * b # (<$) :: a -> Proxy * b -> Proxy * a #
Arrow a => Functor (ArrowMonad a) #	Since: 4.6.0.0
Methods fmap :: (a -> b) -> ArrowMonad a a -> ArrowMonad a b # (<$) :: a -> ArrowMonad a b -> ArrowMonad a a #
Monad m => Functor (WrappedMonad m) #	Since: 2.1
Methods fmap :: (a -> b) -> WrappedMonad m a -> WrappedMonad m b # (<$) :: a -> WrappedMonad m b -> WrappedMonad m a #
Functor (ST s) #	Since: 2.1
Methods fmap :: (a -> b) -> ST s a -> ST s b # (<$) :: a -> ST s b -> ST s a #
Functor (Arg a) #	Since: 4.9.0.0
Methods fmap :: (a -> b) -> Arg a a -> Arg a b # (<$) :: a -> Arg a b -> Arg a a #
Functor f => Functor (Rec1 * f) #
Methods fmap :: (a -> b) -> Rec1 * f a -> Rec1 * f b # (<$) :: a -> Rec1 * f b -> Rec1 * f a #
Functor (URec * Char) #
Methods fmap :: (a -> b) -> URec * Char a -> URec * Char b # (<$) :: a -> URec * Char b -> URec * Char a #
Functor (URec * Double) #
Methods fmap :: (a -> b) -> URec * Double a -> URec * Double b # (<$) :: a -> URec * Double b -> URec * Double a #
Functor (URec * Float) #
Methods fmap :: (a -> b) -> URec * Float a -> URec * Float b # (<$) :: a -> URec * Float b -> URec * Float a #
Functor (URec * Int) #
Methods fmap :: (a -> b) -> URec * Int a -> URec * Int b # (<$) :: a -> URec * Int b -> URec * Int a #
Functor (URec * Word) #
Methods fmap :: (a -> b) -> URec * Word a -> URec * Word b # (<$) :: a -> URec * Word b -> URec * Word a #
Functor (URec * (Ptr ())) #
Methods fmap :: (a -> b) -> URec * (Ptr ()) a -> URec * (Ptr ()) b # (<$) :: a -> URec * (Ptr ()) b -> URec * (Ptr ()) a #
Functor f => Functor (Alt * f) #
Methods fmap :: (a -> b) -> Alt * f a -> Alt * f b # (<$) :: a -> Alt * f b -> Alt * f a #
Functor (Const * m) #	Since: 2.1
Methods fmap :: (a -> b) -> Const * m a -> Const * m b # (<$) :: a -> Const * m b -> Const * m a #
Arrow a => Functor (WrappedArrow a b) #	Since: 2.1
Methods fmap :: (a -> b) -> WrappedArrow a b a -> WrappedArrow a b b # (<$) :: a -> WrappedArrow a b b -> WrappedArrow a b a #
Functor ((->) LiftedRep LiftedRep r) #	Since: 2.1
Methods fmap :: (a -> b) -> (LiftedRep -> LiftedRep) r a -> (LiftedRep -> LiftedRep) r b # (<$) :: a -> (LiftedRep -> LiftedRep) r b -> (LiftedRep -> LiftedRep) r a #
Functor (K1 * i c) #
Methods fmap :: (a -> b) -> K1 * i c a -> K1 * i c b # (<$) :: a -> K1 * i c b -> K1 * i c a #
(Functor g, Functor f) => Functor ((:+:) * f g) #
Methods fmap :: (a -> b) -> (* :+: f) g a -> (* :+: f) g b # (<$) :: a -> (* :+: f) g b -> (* :+: f) g a #
(Functor g, Functor f) => Functor ((::) f g) #
Methods fmap :: (a -> b) -> (* :: f) g a -> ( :: f) g b # (<$) :: a -> ( :: f) g b -> ( :*: f) g a #
(Functor f, Functor g) => Functor (Sum * f g) #	Since: 4.9.0.0
Methods fmap :: (a -> b) -> Sum * f g a -> Sum * f g b # (<$) :: a -> Sum * f g b -> Sum * f g a #
(Functor f, Functor g) => Functor (Product * f g) #	Since: 4.9.0.0
Methods fmap :: (a -> b) -> Product * f g a -> Product * f g b # (<$) :: a -> Product * f g b -> Product * f g a #
Functor f => Functor (M1 * i c f) #
Methods fmap :: (a -> b) -> M1 * i c f a -> M1 * i c f b # (<$) :: a -> M1 * i c f b -> M1 * i c f a #
(Functor g, Functor f) => Functor ((:.:) * * f g) #
Methods fmap :: (a -> b) -> (* :.: ) f g a -> ( :.: ) f g b # (<$) :: a -> ( :.: ) f g b -> ( :.: *) f g a #
(Functor f, Functor g) => Functor (Compose * * f g) #	Since: 4.9.0.0
Methods fmap :: (a -> b) -> Compose * * f g a -> Compose * * f g b # (<$) :: a -> Compose * * f g b -> Compose * * f g a #

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

(>>=) :: forall a b. 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.

(>>) :: forall a b. m a -> m b -> m b infixl 1 #

Sequentially compose two actions, discarding any value produced by the first, like sequencing operators (such as the semicolon) in imperative languages.

return :: a -> m a #

Inject a value into the monadic type.

fail :: String -> m a #

Fail with a message. This operation is not part of the mathematical definition of a monad, but is invoked on pattern-match failure in a do expression.

As part of the MonadFail proposal (MFP), this function is moved to its own class MonadFail (see Control.Monad.Fail for more details). The definition here will be removed in a future release.

Instances

Monad [] #	Since: 2.1
Methods (>>=) :: [a] -> (a -> [b]) -> [b] # (>>) :: [a] -> [b] -> [b] # return :: a -> [a] # fail :: String -> [a] #
Monad Maybe #	Since: 2.1
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: 2.1
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: 4.9.0.0
Methods (>>=) :: Par1 a -> (a -> Par1 b) -> Par1 b # (>>) :: Par1 a -> Par1 b -> Par1 b # return :: a -> Par1 a # fail :: String -> Par1 a #
Monad ReadP #	Since: 2.1
Methods (>>=) :: ReadP a -> (a -> ReadP b) -> ReadP b # (>>) :: ReadP a -> ReadP b -> ReadP b # return :: a -> ReadP a # fail :: String -> ReadP a #
Monad ReadPrec #	Since: 2.1
Methods (>>=) :: ReadPrec a -> (a -> ReadPrec b) -> ReadPrec b # (>>) :: ReadPrec a -> ReadPrec b -> ReadPrec b # return :: a -> ReadPrec a # fail :: String -> ReadPrec a #
Monad Last #
Methods (>>=) :: Last a -> (a -> Last b) -> Last b # (>>) :: Last a -> Last b -> Last b # return :: a -> Last a # fail :: String -> Last a #
Monad First #
Methods (>>=) :: First a -> (a -> First b) -> First b # (>>) :: First a -> First b -> First b # return :: a -> First a # fail :: String -> First a #
Monad Product #	Since: 4.8.0.0
Methods (>>=) :: Product a -> (a -> Product b) -> Product b # (>>) :: Product a -> Product b -> Product b # return :: a -> Product a # fail :: String -> Product a #
Monad Sum #	Since: 4.8.0.0
Methods (>>=) :: Sum a -> (a -> Sum b) -> Sum b # (>>) :: Sum a -> Sum b -> Sum b # return :: a -> Sum a # fail :: String -> Sum a #
Monad Dual #	Since: 4.8.0.0
Methods (>>=) :: Dual a -> (a -> Dual b) -> Dual b # (>>) :: Dual a -> Dual b -> Dual b # return :: a -> Dual a # fail :: String -> Dual a #
Monad STM #	Since: 4.3.0.0
Methods (>>=) :: STM a -> (a -> STM b) -> STM b # (>>) :: STM a -> STM b -> STM b # return :: a -> STM a # fail :: String -> STM a #
Monad Identity #	Since: 4.8.0.0
Methods (>>=) :: Identity a -> (a -> Identity b) -> Identity b # (>>) :: Identity a -> Identity b -> Identity b # return :: a -> Identity a # fail :: String -> Identity a #
Monad NonEmpty #	Since: 4.9.0.0
Methods (>>=) :: NonEmpty a -> (a -> NonEmpty b) -> NonEmpty b # (>>) :: NonEmpty a -> NonEmpty b -> NonEmpty b # return :: a -> NonEmpty a # fail :: String -> NonEmpty a #
Monad Option #	Since: 4.9.0.0
Methods (>>=) :: Option a -> (a -> Option b) -> Option b # (>>) :: Option a -> Option b -> Option b # return :: a -> Option a # fail :: String -> Option a #
Monad Last #	Since: 4.9.0.0
Methods (>>=) :: Last a -> (a -> Last b) -> Last b # (>>) :: Last a -> Last b -> Last b # return :: a -> Last a # fail :: String -> Last a #
Monad First #	Since: 4.9.0.0
Methods (>>=) :: First a -> (a -> First b) -> First b # (>>) :: First a -> First b -> First b # return :: a -> First a # fail :: String -> First a #
Monad Max #	Since: 4.9.0.0
Methods (>>=) :: Max a -> (a -> Max b) -> Max b # (>>) :: Max a -> Max b -> Max b # return :: a -> Max a # fail :: String -> Max a #
Monad Min #	Since: 4.9.0.0
Methods (>>=) :: Min a -> (a -> Min b) -> Min b # (>>) :: Min a -> Min b -> Min b # return :: a -> Min a # fail :: String -> Min a #
Monad Complex #	Since: 4.9.0.0
Methods (>>=) :: Complex a -> (a -> Complex b) -> Complex b # (>>) :: Complex a -> Complex b -> Complex b # return :: a -> Complex a # fail :: String -> Complex a #
Monad (Either e) #	Since: 4.4.0.0
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: 4.9.0.0
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: 4.9.0.0
Methods (>>=) :: (a, a) -> (a -> (a, b)) -> (a, b) # (>>) :: (a, a) -> (a, b) -> (a, b) # return :: a -> (a, a) # fail :: String -> (a, a) #
Monad (ST s) #	Since: 2.1
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 (Proxy *) #	Since: 4.7.0.0
Methods (>>=) :: Proxy * a -> (a -> Proxy * b) -> Proxy * b # (>>) :: Proxy * a -> Proxy * b -> Proxy * b # return :: a -> Proxy * a # fail :: String -> Proxy * a #
ArrowApply a => Monad (ArrowMonad a) #	Since: 2.1
Methods (>>=) :: ArrowMonad a a -> (a -> ArrowMonad a b) -> ArrowMonad a b # (>>) :: ArrowMonad a a -> ArrowMonad a b -> ArrowMonad a b # return :: a -> ArrowMonad a a # fail :: String -> ArrowMonad a a #
Monad m => Monad (WrappedMonad m) #
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 #
Monad (ST s) #	Since: 2.1
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 f => Monad (Rec1 * f) #	Since: 4.9.0.0
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 f => Monad (Alt * f) #
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 ((->) LiftedRep LiftedRep r) #	Since: 2.1
Methods (>>=) :: (LiftedRep -> LiftedRep) r a -> (a -> (LiftedRep -> LiftedRep) r b) -> (LiftedRep -> LiftedRep) r b # (>>) :: (LiftedRep -> LiftedRep) r a -> (LiftedRep -> LiftedRep) r b -> (LiftedRep -> LiftedRep) r b # return :: a -> (LiftedRep -> LiftedRep) r a # fail :: String -> (LiftedRep -> LiftedRep) r a #
(Monad f, Monad g) => Monad ((::) f g) #	Since: 4.9.0.0
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: 4.9.0.0
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 f => Monad (M1 * i c f) #	Since: 4.9.0.0
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 #