Functional style programming tests

oop-to-fp-functional-style-tests.js

let c1 = circle([2.5, 0], 1.5);
let c2 = circle([-2, 0], 2);
const c2ref = c2; // Use a reference to c2 at this point in time

area(c1.r); // -> 7.0685834705770345
area(c2.r); // -> 12.566370614359172

let hit;
[hit, c1, c2] = intersect(c1, c2);
hit; // -> false
c1.hits; // -> 0

c1 = setPos(c1, [1, 0]);
[hit, c1, c2] = intersect(c1, c2);
hit; // -> true
c1.hits; // -> 1
c2.hits; // -> 1

c2ref.hits; // -> 0. The ref is pointing to the initial c2

c1.hits = 4;
c1.hits; // -> 4. This is not great. Mutation is possible.