{-# 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---- Functors: uniform action over a parameterized type, generalizing the-- 'Data.List.map' function on lists.moduleData.Functor(Functor (fmap ),(<$ ),($> ),(<$> ),(<&> ),void ,)whereimportGHC.Base (Functor (..),flip )-- $setup-- Allow the use of Prelude in doctests.-- >>> import Prelude hiding ((<$>))infixl4<$> -- | An infix synonym for 'fmap'.---- The name of this operator is an allusion to '$'.-- 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)--(<$>)::Functor f =>(a ->b )->f a ->f b (<$> )=fmap infixl4$> -- | Flipped version of '<$>'.---- @-- ('<&>') = '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 as<&> f =f <$> asinfixl1<&> -- | Flipped version of '<$'.---- @since 4.7.0.0---- ==== __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) $> "foo"-- (1,"foo")--($>)::Functor f =>f a ->b ->f b ($> )=flip (<$ )-- | @'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 @'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 'System.IO.IO' action:---- >>> mapM print [1,2]-- 1-- 2-- [(),()]-- >>> void $ mapM print [1,2]-- 1-- 2--void::Functor f =>f a ->f ()void x =()<$ x