fn memoize(f) {
    let map = {};
    return fn(x) {
        if has(map, x) {
            return map[x];
        } else {
            let result = f(x);
            map[x] = result;
            return result;
        }
    };
}

fn fib(n) {
    if n <= 1 {
        return n;
    } else {
        return fib(n-1) + fib(n-2);
    }
}

for n: [10,20,25] {
    let start_time = time();
    let result = fib(n);
    let elapsed = time() - start_time;
    println("time for fib(" + str(n) + ")=" + str(result) + ": " + str(elapsed));
}

let fib = memoize(fib);

for n: [10,20,25] {
    let start_time = time();
    let result = fib(n);
    let elapsed = time() - start_time;
    println("time for memoized fib(" + str(n) + ")=" + str(result) + ": " + str(elapsed));
}