{-# LANGUAGE Trustworthy #-}{-# LANGUAGE NoImplicitPrelude #-}------------------------------------------------------------------------------- |-- Module : Data.Functor-- Copyright : (c) The University of Glasgow 2001-- License : BSD-style (see the file libraries/base/LICENSE)---- Maintainer : libraries@haskell.org-- Stability : provisional-- Portability : portable------ A type @f@ is a Functor if it provides a function @fmap@ which, given any types @a@ and @b@,-- lets you apply any function of type @(a -> b)@ to turn an @f a@ into an @f b@, preserving the-- structure of @f@.---- ==== __Examples__---- >>> fmap show (Just 1) -- (a -> b) -> f a -> f b-- Just "1" -- (Int -> String) -> Maybe Int -> Maybe String---- >>> fmap show Nothing -- (a -> b) -> f a -> f b-- Nothing -- (Int -> String) -> Maybe Int -> Maybe String---- >>> fmap show [1,2,3] -- (a -> b) -> f a -> f b-- ["1","2","3"] -- (Int -> String) -> [Int] -> [String]---- >>> fmap show [] -- (a -> b) -> f a -> f b-- [] -- (Int -> String) -> [Int] -> [String]---- The 'fmap' function is also available as the infix operator '<$>':---- >>> fmap show (Just 1) -- (Int -> String) -> Maybe Int -> Maybe String-- Just "1"-- >>> show <$> (Just 1) -- (Int -> String) -> Maybe Int -> Maybe String-- Just "1"moduleData.Functor(Functor (..),($>) ,(<$>) ,(<&>) ,void ,)whereimportGHC.Base (Functor (..),flip )-- $setup-- Allow the use of Prelude in doctests.-- >>> import Prelude hiding ((<$>))infixl4<$> -- | An infix synonym for 'fmap'.---- The name of this operator is an allusion to 'Prelude.$'.-- Note the similarities between their types:---- > ($) :: (a -> b) -> a -> b-- > (<$>) :: Functor f => (a -> b) -> f a -> f b---- Whereas 'Prelude.$' is function application, '<$>' is function-- application lifted over a 'Functor'.---- ==== __Examples__---- Convert from a @'Data.Maybe.Maybe' 'Data.Int.Int'@ to a @'Data.Maybe.Maybe'-- 'Data.String.String'@ using 'Prelude.show':---- >>> show <$> Nothing-- Nothing-- >>> show <$> Just 3-- Just "3"---- Convert from an @'Data.Either.Either' 'Data.Int.Int' 'Data.Int.Int'@ to an-- @'Data.Either.Either' 'Data.Int.Int'@ 'Data.String.String' using 'Prelude.show':---- >>> show <$> Left 17-- Left 17-- >>> show <$> Right 17-- Right "17"---- Double each element of a list:---- >>> (*2) <$> [1,2,3]-- [2,4,6]---- Apply 'Prelude.even' to the second element of a pair:---- >>> even <$> (2,2)-- (2,True)--(<$>) ::Functor f =>(a ->b )->f a ->f b <$> :: forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
(<$>) =(a -> b) -> f a -> f b
forall a b. (a -> b) -> f a -> f b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap infixl1<&> -- | Flipped version of '<$>'.---- @-- ('<&>') = 'flip' 'fmap'-- @---- @since 4.11.0.0---- ==== __Examples__-- Apply @(+1)@ to a list, a 'Data.Maybe.Just' and a 'Data.Either.Right':---- >>> Just 2 <&> (+1)-- Just 3---- >>> [1,2,3] <&> (+1)-- [2,3,4]---- >>> Right 3 <&> (+1)-- Right 4--(<&>) ::Functor f =>f a ->(a ->b )->f b f a
as <&> :: forall (f :: * -> *) a b. Functor f => f a -> (a -> b) -> f b
<&> a -> b
f =a -> b
f (a -> b) -> f a -> f b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> f a
as infixl4$> -- | Flipped version of '<$'.---- @since 4.7.0.0---- ==== __Examples__---- Replace the contents of a @'Data.Maybe.Maybe' 'Data.Int.Int'@ with a constant-- 'Data.String.String':---- >>> Nothing $> "foo"-- Nothing-- >>> Just 90210 $> "foo"-- Just "foo"---- Replace the contents of an @'Data.Either.Either' 'Data.Int.Int' 'Data.Int.Int'@-- with a constant 'Data.String.String', resulting in an @'Data.Either.Either'-- 'Data.Int.Int' 'Data.String.String'@:---- >>> Left 8675309 $> "foo"-- Left 8675309-- >>> Right 8675309 $> "foo"-- Right "foo"---- Replace each element of a list with a constant 'Data.String.String':---- >>> [1,2,3] $> "foo"-- ["foo","foo","foo"]---- Replace the second element of a pair with a constant 'Data.String.String':---- >>> (1,2) $> "foo"-- (1,"foo")--($>) ::Functor f =>f a ->b ->f b $> :: forall (f :: * -> *) a b. Functor f => f a -> b -> f b
($>) =(b -> f a -> f b) -> f a -> b -> f b
forall a b c. (a -> b -> c) -> b -> a -> c
flip b -> f a -> f b
forall a b. a -> f b -> f a
forall (f :: * -> *) a b. Functor f => a -> f b -> f a
(<$) -- | @'void' value@ discards or ignores the result of evaluation, such-- as the return value of an 'System.IO.IO' action.---- ==== __Examples__---- Replace the contents of a @'Data.Maybe.Maybe' 'Data.Int.Int'@ with unit:---- >>> void Nothing-- Nothing-- >>> void (Just 3)-- Just ()---- Replace the contents of an @'Data.Either.Either' 'Data.Int.Int' 'Data.Int.Int'@-- with unit, resulting in an @'Data.Either.Either' 'Data.Int.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 'System.IO.IO' action:---- >>> mapM print [1,2]-- 1-- 2-- [(),()]-- >>> void $ mapM print [1,2]-- 1-- 2--void ::Functor f =>f a ->f ()void :: forall (f :: * -> *) a. Functor f => f a -> f ()
void f a
x =()() -> f a -> f ()
forall a b. a -> f b -> f a
forall (f :: * -> *) a b. Functor f => a -> f b -> f a
<$ f a
x