Going functional

This tutorial introduces functional programming by starting with a very simple problem description.

Javascript is used as the language to demonstrate this, but the principal can be applied to most programming languages.

Problem to solve

Given two lists of numbers, define a function that takes 2 lists as parameters and computes the cross sum of the numbers.

For example:

var list1 = [11, 19, 10];
var list2 = [11, 17, 12];
var results = crossSumOfTwoArrays(list1, list2);

should return:

[22, 28, 23, 30, 36, 31, 21, 27, 22];

This means that we did:

[
    list1[0] + list2[0],
    list1[0] + list2[1],
    list1[0] + list2[2],
    list1[1] + list2[0],
    list1[1] + list2[1],
    list1[1] + list2[2],
    list1[2] + list2[0],
    list1[2] + list2[1],
    list1[2] + list2[2]
]

Let's begin with the smartass.