fn cartesian<F, G, I, J, T, U>(x: F, y: G) -> Vec<(T, U)>
where
    I: IntoIterator<Item=T>,
    J: IntoIterator<Item=U>,
    F: Fn() -> I,
    G: Fn() -> J
{
    x().into_iter().map(
        |xp| y().into_iter().map(
            |yp| (xp, yp)
        )
    ).flat_map(|i| i).collect()
}

fn main() {
    let v1 = vec![String::from("foo"), String::from("bar")];
    let v2 = vec![String::from("baz"), String::from("qux")];

    let it = cartesian(|| v1.iter(), || v2.iter());

    for item in it {
        let (s1, s2) = item;
        println!("{} {}", s1, s2)
    }
}