pub fn each_in_circle(x: i32, y: i32, r: i32, mut callback: impl FnMut(i32, i32)) {
    for cy in (-r) ..= r {
        for cx in (-r)..=r {
            if cx * cx + cy * cy <= r * r {
                callback(cx + x, cy + y)
            }
        }
    }
}

fn main() {
    each_in_circle(0, 0, 3, |x, y| {
        println!("{}, {}", x, y);
    })
}