factorialRec(n) {
    if (n == 0) return 1;
    return n * factorialRec(n - 1);
}

factorialIter(n) {
    for (i in range(1, n))
        n *= i;
    return n;
}

factorialFold(n) {
    return reduce(multiply, 1, range(1, n + 1));
}