extern printf = (*i64, varargs) => i64;

let main = () => i64 {
    let factorial = (n: i64) => i64 {
        let f = (acc: i64, n: i64) => i64 {
            if n == 0 {
                return acc;
            };
            return f(acc * n, n - 1);
        };
        return f(1, n);
    };

    let is_even = (n: i64) => bool {
        if n % 2 == 0 {
            return true;
        };
        return false;
    };

    let sum_if = (predicate: (i64) => bool, limit: i64) => i64 {
        let sum = 0;
        let i = 0;
        while i < limit {
            if predicate(i) {
                sum = sum + i;
            };
            i = i + 1;
        };
        return sum;
    };

    let fact_val = factorial(6);
    printf("%d", fact_val);

    let even_sum = sum_if(is_even, 20);
    printf("%d", even_sum);

    return 0;
};