fn main() {
    let responders = vec![];
    responders.push(|req: &str| { Option::<String>::None });
    responders.push(|req: &str| { Some("Asdf".to_string()) });
    let c = 5u64;
    let f: fn(u64, u64) -> u64 = |a, b| { a + b + c };
    println!("1 + 2 = {}", f(1, 2));
}