Function fib4

test/README.example.spec.ts:1386–1389

(n: number)

    };

    const fib4 = (n: number): Effected<never, number> => {
      if (n <= 1) return Effected.of(n);
      return fib4(n - 1).flatMap((a) => fib4(n - 2).map((b) => a + b));
    };

    expect(fib1(10).runSync()).toBe(55);
    expect(fib2(10).runSync()).toBe(55);