fn main() {
    println!("Hello, world!");

    let list = [1,2,3,4];

    dbg!(foo(&list, 2));
}

fn foo<T: Clone+std::fmt::Debug>(list: &[T], n: usize) -> Vec<Vec<T>> {
    let mut ret = Vec::new();

    if list.len() == n {
        ret.push(list.to_vec());
    } else if n == 1 {
        ret.extend(list.iter().map(|i| vec![i.clone()]));
    } else {

        for first_i in 0..list.len()-n+1 {
            let results = foo(&list[first_i+1..],n-1);

            for mut r in results {
                r.push(list[first_i].clone());
                ret.push(r);
            }
        }
    }

    ret
}