base-4.10.1.0: Basic libraries

Data.Functor

Description

Functors: uniform action over a parameterized type, generalizing the map function on lists.

Synopsis

# Documentation

class Functor f where Source #

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 Source #

(<$) :: a -> f b -> f a infixl 4 Source # Replace all locations in the input with the same value. The default definition is fmap . const, but this may be overridden with a more efficient version. Instances  Functor [] Source # Since: 2.1 Methodsfmap :: (a -> b) -> [a] -> [b] Source #(<$) :: a -> [b] -> [a] Source # Source # Since: 2.1 Methodsfmap :: (a -> b) -> Maybe a -> Maybe b Source #(<$) :: a -> Maybe b -> Maybe a Source # Source # Since: 2.1 Methodsfmap :: (a -> b) -> IO a -> IO b Source #(<$) :: a -> IO b -> IO a Source # Source # Methodsfmap :: (a -> b) -> Par1 a -> Par1 b Source #(<$) :: a -> Par1 b -> Par1 a Source # Source # Since: 2.1 Methodsfmap :: (a -> b) -> ReadP a -> ReadP b Source #(<$) :: a -> ReadP b -> ReadP a Source # Source # Since: 2.1 Methodsfmap :: (a -> b) -> ReadPrec a -> ReadPrec b Source #(<$) :: a -> ReadPrec b -> ReadPrec a Source # Source # Methodsfmap :: (a -> b) -> Last a -> Last b Source #(<$) :: a -> Last b -> Last a Source # Source # Methodsfmap :: (a -> b) -> First a -> First b Source #(<$) :: a -> First b -> First a Source # Source # Since: 4.8.0.0 Methodsfmap :: (a -> b) -> Product a -> Product b Source #(<$) :: a -> Product b -> Product a Source # Source # Since: 4.8.0.0 Methodsfmap :: (a -> b) -> Sum a -> Sum b Source #(<$) :: a -> Sum b -> Sum a Source # Source # Since: 4.8.0.0 Methodsfmap :: (a -> b) -> Dual a -> Dual b Source #(<$) :: a -> Dual b -> Dual a Source # Source # Since: 4.3.0.0 Methodsfmap :: (a -> b) -> STM a -> STM b Source #(<$) :: a -> STM b -> STM a Source # Source # Since: 4.6.0.0 Methodsfmap :: (a -> b) -> Handler a -> Handler b Source #(<$) :: a -> Handler b -> Handler a Source # Source # Since: 4.8.0.0 Methodsfmap :: (a -> b) -> Identity a -> Identity b Source #(<$) :: a -> Identity b -> Identity a Source # Source # Methodsfmap :: (a -> b) -> ZipList a -> ZipList b Source #(<$) :: a -> ZipList b -> ZipList a Source # Source # Since: 4.6.0.0 Methodsfmap :: (a -> b) -> ArgDescr a -> ArgDescr b Source #(<$) :: a -> ArgDescr b -> ArgDescr a Source # Source # Since: 4.6.0.0 Methodsfmap :: (a -> b) -> OptDescr a -> OptDescr b Source #(<$) :: a -> OptDescr b -> OptDescr a Source # Source # Since: 4.6.0.0 Methodsfmap :: (a -> b) -> ArgOrder a -> ArgOrder b Source #(<$) :: a -> ArgOrder b -> ArgOrder a Source # Source # Since: 4.9.0.0 Methodsfmap :: (a -> b) -> NonEmpty a -> NonEmpty b Source #(<$) :: a -> NonEmpty b -> NonEmpty a Source # Source # Since: 4.9.0.0 Methodsfmap :: (a -> b) -> Option a -> Option b Source #(<$) :: a -> Option b -> Option a Source # Source # Since: 4.9.0.0 Methodsfmap :: (a -> b) -> Last a -> Last b Source #(<$) :: a -> Last b -> Last a Source # Source # Since: 4.9.0.0 Methodsfmap :: (a -> b) -> First a -> First b Source #(<$) :: a -> First b -> First a Source # Source # Since: 4.9.0.0 Methodsfmap :: (a -> b) -> Max a -> Max b Source #(<$) :: a -> Max b -> Max a Source # Source # Since: 4.9.0.0 Methodsfmap :: (a -> b) -> Min a -> Min b Source #(<$) :: a -> Min b -> Min a Source # Source # Methodsfmap :: (a -> b) -> Complex a -> Complex b Source #(<$) :: a -> Complex b -> Complex a Source # Source # Since: 3.0 Methodsfmap :: (a -> b) -> Either a a -> Either a b Source #(<$) :: a -> Either a b -> Either a a Source # Source # Methodsfmap :: (a -> b) -> V1 * a -> V1 * b Source #(<$) :: a -> V1 * b -> V1 * a Source # Source # Since: 4.9.0.0 Methodsfmap :: (a -> b) -> U1 * a -> U1 * b Source #(<$) :: a -> U1 * b -> U1 * a Source # Functor ((,) a) Source # Since: 2.1 Methodsfmap :: (a -> b) -> (a, a) -> (a, b) Source #(<$) :: a -> (a, b) -> (a, a) Source # Functor (ST s) Source # Since: 2.1 Methodsfmap :: (a -> b) -> ST s a -> ST s b Source #(<$) :: a -> ST s b -> ST s a Source # Source # Since: 4.7.0.0 Methodsfmap :: (a -> b) -> Proxy * a -> Proxy * b Source #(<$) :: a -> Proxy * b -> Proxy * a Source # Arrow a => Functor (ArrowMonad a) Source # Since: 4.6.0.0 Methodsfmap :: (a -> b) -> ArrowMonad a a -> ArrowMonad a b Source #(<$) :: a -> ArrowMonad a b -> ArrowMonad a a Source # Monad m => Functor (WrappedMonad m) Source # Since: 2.1 Methodsfmap :: (a -> b) -> WrappedMonad m a -> WrappedMonad m b Source #(<$) :: a -> WrappedMonad m b -> WrappedMonad m a Source # Functor (ST s) Source # Since: 2.1 Methodsfmap :: (a -> b) -> ST s a -> ST s b Source #(<$) :: a -> ST s b -> ST s a Source # Functor (Arg a) Source # Since: 4.9.0.0 Methodsfmap :: (a -> b) -> Arg a a -> Arg a b Source #(<$) :: a -> Arg a b -> Arg a a Source # Functor f => Functor (Rec1 * f) Source # Methodsfmap :: (a -> b) -> Rec1 * f a -> Rec1 * f b Source #(<$) :: a -> Rec1 * f b -> Rec1 * f a Source # Source # Methodsfmap :: (a -> b) -> URec * Char a -> URec * Char b Source #(<$) :: a -> URec * Char b -> URec * Char a Source # Source # Methodsfmap :: (a -> b) -> URec * Double a -> URec * Double b Source #(<$) :: a -> URec * Double b -> URec * Double a Source # Source # Methodsfmap :: (a -> b) -> URec * Float a -> URec * Float b Source #(<$) :: a -> URec * Float b -> URec * Float a Source # Source # Methodsfmap :: (a -> b) -> URec * Int a -> URec * Int b Source #(<$) :: a -> URec * Int b -> URec * Int a Source # Source # Methodsfmap :: (a -> b) -> URec * Word a -> URec * Word b Source #(<$) :: a -> URec * Word b -> URec * Word a Source # Functor (URec * (Ptr ())) Source # Methodsfmap :: (a -> b) -> URec * (Ptr ()) a -> URec * (Ptr ()) b Source #(<$) :: a -> URec * (Ptr ()) b -> URec * (Ptr ()) a Source # Functor f => Functor (Alt * f) Source # Methodsfmap :: (a -> b) -> Alt * f a -> Alt * f b Source #(<$) :: a -> Alt * f b -> Alt * f a Source # Source # Since: 2.1 Methodsfmap :: (a -> b) -> Const * m a -> Const * m b Source #(<$) :: a -> Const * m b -> Const * m a Source # Arrow a => Functor (WrappedArrow a b) Source # Since: 2.1 Methodsfmap :: (a -> b) -> WrappedArrow a b a -> WrappedArrow a b b Source #(<$) :: a -> WrappedArrow a b b -> WrappedArrow a b a Source # Functor ((->) LiftedRep LiftedRep r) Source # Since: 2.1 Methodsfmap :: (a -> b) -> (LiftedRep -> LiftedRep) r a -> (LiftedRep -> LiftedRep) r b Source #(<$) :: a -> (LiftedRep -> LiftedRep) r b -> (LiftedRep -> LiftedRep) r a Source # Functor (K1 * i c) Source # Methodsfmap :: (a -> b) -> K1 * i c a -> K1 * i c b Source #(<$) :: a -> K1 * i c b -> K1 * i c a Source # (Functor g, Functor f) => Functor ((:+:) * f g) Source # Methodsfmap :: (a -> b) -> (* :+: f) g a -> (* :+: f) g b Source #(<$) :: a -> (* :+: f) g b -> (* :+: f) g a Source # (Functor g, Functor f) => Functor ((:*:) * f g) Source # Methodsfmap :: (a -> b) -> (* :*: f) g a -> (* :*: f) g b Source #(<$) :: a -> (* :*: f) g b -> (* :*: f) g a Source # (Functor f, Functor g) => Functor (Sum * f g) Source # Since: 4.9.0.0 Methodsfmap :: (a -> b) -> Sum * f g a -> Sum * f g b Source #(<$) :: a -> Sum * f g b -> Sum * f g a Source # (Functor f, Functor g) => Functor (Product * f g) Source # Since: 4.9.0.0 Methodsfmap :: (a -> b) -> Product * f g a -> Product * f g b Source #(<$) :: a -> Product * f g b -> Product * f g a Source # Functor f => Functor (M1 * i c f) Source # Methodsfmap :: (a -> b) -> M1 * i c f a -> M1 * i c f b Source #(<$) :: a -> M1 * i c f b -> M1 * i c f a Source # (Functor g, Functor f) => Functor ((:.:) * * f g) Source # Methodsfmap :: (a -> b) -> (* :.: *) f g a -> (* :.: *) f g b Source #(<$) :: a -> (* :.: *) f g b -> (* :.: *) f g a Source # (Functor f, Functor g) => Functor (Compose * * f g) Source # Since: 4.9.0.0 Methodsfmap :: (a -> b) -> Compose * * f g a -> Compose * * f g b Source #(<$) :: a -> Compose * * f g b -> Compose * * f g a Source # (<$) :: Functor f => a -> f b -> f a infixl 4 Source #

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.

($>) :: Functor f => f a -> b -> f b infixl 4 Source # Flipped version of <$.

#### Examples

Replace the contents of a Maybe Int with a constant String:

>>> Nothing $> "foo" Nothing >>> Just 90210$> "foo"
Just "foo"


Replace the contents of an Either Int Int with a constant String, resulting in an Either Int String:

>>> Left 8675309 $> "foo" Left 8675309 >>> Right 8675309$> "foo"
Right "foo"


Replace each element of a list with a constant String:

>>> [1,2,3] $> "foo" ["foo","foo","foo"]  Replace the second element of a pair with a constant String: >>> (1,2)$> "foo"
(1,"foo")


Since: 4.7.0.0

(<$>) :: Functor f => (a -> b) -> f a -> f b infixl 4 Source # An infix synonym for fmap. The name of this operator is an allusion to $. Note the similarities between their types:

 ($) :: (a -> b) -> a -> b (<$>) :: Functor f => (a -> b) -> f a -> f b

Whereas $ is function application, <$> is function application lifted over a Functor.

#### Examples

Convert from a Maybe Int to a Maybe String using show:

>>> show <$> Nothing Nothing >>> show <$> Just 3
Just "3"


Convert from an Either Int Int to an Either Int String using show:

>>> show <$> Left 17 Left 17 >>> show <$> Right 17
Right "17"


Double each element of a list:

>>> (*2) <$> [1,2,3] [2,4,6]  Apply even to the second element of a pair: >>> even <$> (2,2)
(2,True)


void :: Functor f => f a -> f () Source #

void value discards or ignores the result of evaluation, such as the return value of an IO action.

#### Examples

Replace the contents of a Maybe Int with unit:

>>> void Nothing
Nothing
>>> void (Just 3)
Just ()


Replace the contents of an Either Int Int with unit, resulting in an Either Int '()':

>>> void (Left 8675309)
Left 8675309
>>> void (Right 8675309)
Right ()


Replace every element of a list with unit:

>>> void [1,2,3]
[(),(),()]


Replace the second element of a pair with unit:

>>> void (1,2)
(1,())


Discard the result of an IO action:

>>> mapM print [1,2]
1
2
[(),()]
>>> void \$ mapM print [1,2]
1
2