freeCodeCamp/guide/english/haskell/map/index.md

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map function

map function

The map function is a built-in haskell's function that maps a function to each element of a list and return a new list with the result. Graphically, it would look like this.

map f [1,2,3,4]
-- [f 1, f 2, f 3, f 4]

Signature of map

The signature of the map function is as follows

map :: (a -> b) -> [a] -> [b]

Examples

map succ [1..5]
-- [2,3,4,5,6]

let sample = [(1, 2), (3, 1), (4, 10)]
map fst sample
-- [1,3,4]

map snd sample
-- [2,1,10]

import Data.Char (toLower) # to get the toLower
map toLower "HELLO WORLD HASKELL RULEZ!"
-- "hello world haskell rulez!"