Quelles sont les deux lois que doit satisfaire un functor ?

const map = <A, B>(arr: A[], fn: (a: A) => B): B[] =>
  arr.map(fn);

const identity = <T>(x: T): T => x;
const double = (x: number) => x * 2;
const addOne = (x: number) => x + 1;

// Law 1: Identity
map([1, 2, 3], identity) // === [1, 2, 3]

// Law 2: Composition
map(map([1, 2, 3], double), addOne)
// === 
map([1, 2, 3], x => addOne(double(x)))