fn gen_primes() -> impl Iterator<Item = u32> {
    fn is_prime(x: &u32) -> bool { // note: `&u32` is not idiomatic, but makes things cleaner below. Good enough for a POC :)
        false
    }
    (2..).filter(is_prime)
}

fn main() {
    println!(
        "{:?}",
        gen_primes().take_while(|x| *x < 50).collect::<Vec<_>>()
    );
}