Mockingbird Combinator

Self-application combinator. Applies a function to itself. Forms the basis of recursion in lambda calculus.

export const Mockingbird = (x: Fn) => x(x);
export const M = Mockingbird;
export const SelfApply = M;

const factorial = Mockingbird((f: any) => (n: number) => (n <= 1 ? 1 : n * f(f)(n - 1)));
factorial(5); // 120