Map & Filter

Map & Filter

List.map transforms every element:

let squares = List.map (fun x -> x * x) [1; 2; 3; 4; 5]
// [1; 4; 9; 16; 25]

List.filter keeps elements that satisfy a predicate:

let evens = List.filter (fun x -> x % 2 = 0) [1; 2; 3; 4; 5; 6]
// [2; 4; 6]

Combine them with the pipe operator:

let result =
    [1..10]
    |> List.filter (fun x -> x % 2 <> 0)
    |> List.map (fun x -> x * x)
    |> List.sum
// 1 + 9 + 25 + 49 + 81 = 165

Your Task

Write a function evenSquaresSum that takes a list of integers, keeps the even numbers, squares each, and returns the sum. Use pipes.