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	Trustworthy
Language	Haskell2010

Data.Functor

Description

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

Synopsis

classFunctor fwhere
- fmap :: (a -> b) -> f a -> f b
(<$) ::Functor f => a -> f b -> f a
($>) ::Functor f => f a -> b -> f b
(<$>) ::Functor f => (a -> b) -> f a -> f b
(<&>) ::Functor f => f a -> (a -> b) -> f b
void ::Functor f => f a -> f ()

Documentation

classFunctor fwhereSource #

TheFunctor class is used for types that can be mapped over.Instances ofFunctor should satisfy the following laws:

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

The instances ofFunctor for lists,Maybe andIOsatisfy these laws.

Methods

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

Instances

Functor []Source #	Since: 2.1
Instance details Defined inGHC.Base Methods fmap :: (a -> b) -> [a] -> [b]Source # (<$) :: a -> [b] -> [a]Source #
Functor MaybeSource #	Since: 2.1
Instance details Defined inGHC.Base Methods fmap :: (a -> b) ->Maybe a ->Maybe bSource # (<$) :: a ->Maybe b ->Maybe aSource #
Functor IOSource #	Since: 2.1
Instance details Defined inGHC.Base Methods fmap :: (a -> b) ->IO a ->IO bSource # (<$) :: a ->IO b ->IO aSource #
Functor Par1Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) ->Par1 a ->Par1 bSource # (<$) :: a ->Par1 b ->Par1 aSource #
Functor NonEmptySource #	Since: 4.9.0.0
Instance details Defined inGHC.Base Methods fmap :: (a -> b) ->NonEmpty a ->NonEmpty bSource # (<$) :: a ->NonEmpty b ->NonEmpty aSource #
Functor ReadPSource #	Since: 2.1
Instance details Defined inText.ParserCombinators.ReadP Methods fmap :: (a -> b) ->ReadP a ->ReadP bSource # (<$) :: a ->ReadP b ->ReadP aSource #
Functor ReadPrecSource #	Since: 2.1
Instance details Defined inText.ParserCombinators.ReadPrec Methods fmap :: (a -> b) ->ReadPrec a ->ReadPrec bSource # (<$) :: a ->ReadPrec b ->ReadPrec aSource #
Functor DownSource #	Since: 4.11.0.0
Instance details Defined inData.Ord Methods fmap :: (a -> b) ->Down a ->Down bSource # (<$) :: a ->Down b ->Down aSource #
Functor ProductSource #	Since: 4.8.0.0
Instance details Defined inData.Semigroup.Internal Methods fmap :: (a -> b) ->Product a ->Product bSource # (<$) :: a ->Product b ->Product aSource #
Functor SumSource #	Since: 4.8.0.0
Instance details Defined inData.Semigroup.Internal Methods fmap :: (a -> b) ->Sum a ->Sum bSource # (<$) :: a ->Sum b ->Sum aSource #
Functor DualSource #	Since: 4.8.0.0
Instance details Defined inData.Semigroup.Internal Methods fmap :: (a -> b) ->Dual a ->Dual bSource # (<$) :: a ->Dual b ->Dual aSource #
Functor LastSource #	Since: 4.8.0.0
Instance details Defined inData.Monoid Methods fmap :: (a -> b) ->Last a ->Last bSource # (<$) :: a ->Last b ->Last aSource #
Functor FirstSource #	Since: 4.8.0.0
Instance details Defined inData.Monoid Methods fmap :: (a -> b) ->First a ->First bSource # (<$) :: a ->First b ->First aSource #
Functor STMSource #	Since: 4.3.0.0
Instance details Defined inGHC.Conc.Sync Methods fmap :: (a -> b) ->STM a ->STM bSource # (<$) :: a ->STM b ->STM aSource #
Functor HandlerSource #	Since: 4.6.0.0
Instance details Defined inControl.Exception Methods fmap :: (a -> b) ->Handler a ->Handler bSource # (<$) :: a ->Handler b ->Handler aSource #
Functor IdentitySource #	Since: 4.8.0.0
Instance details Defined inData.Functor.Identity Methods fmap :: (a -> b) ->Identity a ->Identity bSource # (<$) :: a ->Identity b ->Identity aSource #
Functor ZipListSource #	Since: 2.1
Instance details Defined inControl.Applicative Methods fmap :: (a -> b) ->ZipList a ->ZipList bSource # (<$) :: a ->ZipList b ->ZipList aSource #
Functor ArgDescrSource #	Since: 4.6.0.0
Instance details Defined inSystem.Console.GetOpt Methods fmap :: (a -> b) ->ArgDescr a ->ArgDescr bSource # (<$) :: a ->ArgDescr b ->ArgDescr aSource #
Functor OptDescrSource #	Since: 4.6.0.0
Instance details Defined inSystem.Console.GetOpt Methods fmap :: (a -> b) ->OptDescr a ->OptDescr bSource # (<$) :: a ->OptDescr b ->OptDescr aSource #
Functor ArgOrderSource #	Since: 4.6.0.0
Instance details Defined inSystem.Console.GetOpt Methods fmap :: (a -> b) ->ArgOrder a ->ArgOrder bSource # (<$) :: a ->ArgOrder b ->ArgOrder aSource #
Functor OptionSource #	Since: 4.9.0.0
Instance details Defined inData.Semigroup Methods fmap :: (a -> b) ->Option a ->Option bSource # (<$) :: a ->Option b ->Option aSource #
Functor LastSource #	Since: 4.9.0.0
Instance details Defined inData.Semigroup Methods fmap :: (a -> b) ->Last a ->Last bSource # (<$) :: a ->Last b ->Last aSource #
Functor FirstSource #	Since: 4.9.0.0
Instance details Defined inData.Semigroup Methods fmap :: (a -> b) ->First a ->First bSource # (<$) :: a ->First b ->First aSource #
Functor MaxSource #	Since: 4.9.0.0
Instance details Defined inData.Semigroup Methods fmap :: (a -> b) ->Max a ->Max bSource # (<$) :: a ->Max b ->Max aSource #
Functor MinSource #	Since: 4.9.0.0
Instance details Defined inData.Semigroup Methods fmap :: (a -> b) ->Min a ->Min bSource # (<$) :: a ->Min b ->Min aSource #
Functor ComplexSource #	Since: 4.9.0.0
Instance details Defined inData.Complex Methods fmap :: (a -> b) ->Complex a ->Complex bSource # (<$) :: a ->Complex b ->Complex aSource #
Functor (Either a)Source #	Since: 3.0
Instance details Defined inData.Either Methods fmap :: (a0 -> b) ->Either a a0 ->Either a bSource # (<$) :: a0 ->Either a b ->Either a a0Source #
Functor (V1 ::Type ->Type)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) ->V1 a ->V1 bSource # (<$) :: a ->V1 b ->V1 aSource #
Functor (U1 ::Type ->Type)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) ->U1 a ->U1 bSource # (<$) :: a ->U1 b ->U1 aSource #
Functor ((,) a)Source #	Since: 2.1
Instance details Defined inGHC.Base Methods fmap :: (a0 -> b) -> (a, a0) -> (a, b)Source # (<$) :: a0 -> (a, b) -> (a, a0)Source #
Functor (ST s)Source #	Since: 2.1
Instance details Defined inGHC.ST Methods fmap :: (a -> b) ->ST s a ->ST s bSource # (<$) :: a ->ST s b ->ST s aSource #
Functor (Proxy ::Type ->Type)Source #	Since: 4.7.0.0
Instance details Defined inData.Proxy Methods fmap :: (a -> b) ->Proxy a ->Proxy bSource # (<$) :: a ->Proxy b ->Proxy aSource #
Arrow a =>Functor (ArrowMonad a)Source #	Since: 4.6.0.0
Instance details Defined inControl.Arrow Methods fmap :: (a0 -> b) ->ArrowMonad a a0 ->ArrowMonad a bSource # (<$) :: a0 ->ArrowMonad a b ->ArrowMonad a a0Source #
Monad m =>Functor (WrappedMonad m)Source #	Since: 2.1
Instance details Defined inControl.Applicative Methods fmap :: (a -> b) ->WrappedMonad m a ->WrappedMonad m bSource # (<$) :: a ->WrappedMonad m b ->WrappedMonad m aSource #
Functor (ST s)Source #	Since: 2.1
Instance details Defined inControl.Monad.ST.Lazy.Imp Methods fmap :: (a -> b) ->ST s a ->ST s bSource # (<$) :: a ->ST s b ->ST s aSource #
Functor (Arg a)Source #	Since: 4.9.0.0
Instance details Defined inData.Semigroup Methods fmap :: (a0 -> b) ->Arg a a0 ->Arg a bSource # (<$) :: a0 ->Arg a b ->Arg a a0Source #
Functor f =>Functor (Rec1 f)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) ->Rec1 f a ->Rec1 f bSource # (<$) :: a ->Rec1 f b ->Rec1 f aSource #
Functor (URec Char ::Type ->Type)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) ->URec Char a ->URec Char bSource # (<$) :: a ->URec Char b ->URec Char aSource #
Functor (URec Double ::Type ->Type)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) ->URec Double a ->URec Double bSource # (<$) :: a ->URec Double b ->URec Double aSource #
Functor (URec Float ::Type ->Type)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) ->URec Float a ->URec Float bSource # (<$) :: a ->URec Float b ->URec Float aSource #
Functor (URec Int ::Type ->Type)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) ->URec Int a ->URec Int bSource # (<$) :: a ->URec Int b ->URec Int aSource #
Functor (URec Word ::Type ->Type)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) ->URec Word a ->URec Word bSource # (<$) :: a ->URec Word b ->URec Word aSource #
Functor (URec (Ptr ()) ::Type ->Type)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) ->URec (Ptr ()) a ->URec (Ptr ()) bSource # (<$) :: a ->URec (Ptr ()) b ->URec (Ptr ()) aSource #
Functor f =>Functor (Alt f)Source #	Since: 4.8.0.0
Instance details Defined inData.Semigroup.Internal Methods fmap :: (a -> b) ->Alt f a ->Alt f bSource # (<$) :: a ->Alt f b ->Alt f aSource #
Functor f =>Functor (Ap f)Source #	Since: 4.12.0.0
Instance details Defined inData.Monoid Methods fmap :: (a -> b) ->Ap f a ->Ap f bSource # (<$) :: a ->Ap f b ->Ap f aSource #
Functor (Const m ::Type ->Type)Source #	Since: 2.1
Instance details Defined inData.Functor.Const Methods fmap :: (a -> b) ->Const m a ->Const m bSource # (<$) :: a ->Const m b ->Const m aSource #
Arrow a =>Functor (WrappedArrow a b)Source #	Since: 2.1
Instance details Defined inControl.Applicative Methods fmap :: (a0 -> b0) ->WrappedArrow a b a0 ->WrappedArrow a b b0Source # (<$) :: a0 ->WrappedArrow a b b0 ->WrappedArrow a b a0Source #
Functor ((->) r ::Type ->Type)Source #	Since: 2.1
Instance details Defined inGHC.Base Methods fmap :: (a -> b) -> (r -> a) -> r -> bSource # (<$) :: a -> (r -> b) -> r -> aSource #
Functor (K1 i c ::Type ->Type)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) ->K1 i c a ->K1 i c bSource # (<$) :: a ->K1 i c b ->K1 i c aSource #
(Functor f,Functor g) =>Functor (f:+: g)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) -> (f:+: g) a -> (f:+: g) bSource # (<$) :: a -> (f:+: g) b -> (f:+: g) aSource #
(Functor f,Functor g) =>Functor (f:*: g)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) -> (f:: g) a -> (f:: g) bSource # (<$) :: a -> (f:: g) b -> (f:: g) aSource #
(Functor f,Functor g) =>Functor (Sum f g)Source #	Since: 4.9.0.0
Instance details Defined inData.Functor.Sum Methods fmap :: (a -> b) ->Sum f g a ->Sum f g bSource # (<$) :: a ->Sum f g b ->Sum f g aSource #
(Functor f,Functor g) =>Functor (Product f g)Source #	Since: 4.9.0.0
Instance details Defined inData.Functor.Product Methods fmap :: (a -> b) ->Product f g a ->Product f g bSource # (<$) :: a ->Product f g b ->Product f g aSource #
Functor f =>Functor (M1 i c f)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) ->M1 i c f a ->M1 i c f bSource # (<$) :: a ->M1 i c f b ->M1 i c f aSource #
(Functor f,Functor g) =>Functor (f:.: g)Source #	Since: 4.9.0.0
Instance details Defined inGHC.Generics Methods fmap :: (a -> b) -> (f:.: g) a -> (f:.: g) bSource # (<$) :: a -> (f:.: g) b -> (f:.: g) aSource #
(Functor f,Functor g) =>Functor (Compose f g)Source #	Since: 4.9.0.0
Instance details Defined inData.Functor.Compose Methods fmap :: (a -> b) ->Compose f g a ->Compose f g bSource # (<$) :: a ->Compose f g b ->Compose f g aSource #

(<$) ::Functor f => a -> f b -> f ainfixl 4Source #

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

($>) ::Functor f => f a -> b -> f binfixl 4Source #

Flipped version of<$.

Examples

Expand

Replace the contents of aMaybeInt with a constantString:

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

Replace the contents of anEitherIntInt with a constantString, resulting in anEitherIntString:

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

Replace each element of a list with a constantString:

>>>[1,2,3] $> "foo"["foo","foo","foo"]

Replace the second element of a pair with a constantString:

>>>(1,2) $> "foo"(1,"foo")

Since: 4.7.0.0

(<$>) ::Functor f => (a -> b) -> f a -> f binfixl 4Source #

An infix synonym forfmap.

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 aFunctor.

Examples

Expand

Convert from aMaybeInt to aMaybeString usingshow:

>>>show <$> NothingNothing>>>show <$> Just 3Just "3"

Convert from anEitherIntInt to anEitherIntString usingshow:

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

Double each element of a list:

>>>(*2) <$> [1,2,3][2,4,6]

Applyeven to the second element of a pair:

>>>even <$> (2,2)(2,True)

(<&>) ::Functor f => f a -> (a -> b) -> f binfixl 1Source #

Flipped version of<$>.

(<&>) =flipfmap

Examples

Expand

Apply(+1) to a list, aJust and aRight:

>>>Just 2 <&> (+1)Just 3

>>>[1,2,3] <&> (+1)[2,3,4]

>>>Right 3 <&> (+1)Right 4

Since: 4.11.0.0

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

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

Examples

Expand

Replace the contents of aMaybeInt with unit:

>>>void NothingNothing>>>void (Just 3)Just ()

Replace the contents of anEitherIntInt with unit, resulting in anEitherInt '()':

>>>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 anIO action:

>>>mapM print [1,2]12[(),()]>>>void $ mapM print [1,2]12

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