use std::cell::Cell;

fn a(
    k: i32,
    x1: &dyn Fn() -> i32,
    x2: &dyn Fn() -> i32,
    x3: &dyn Fn() -> i32,
    x4: &dyn Fn() -> i32,
    x5: &dyn Fn() -> i32,
) -> i32 {
    let k1 = Cell::new(k);
    struct B<'a> {
        f: &'a dyn Fn(&B) -> i32,
    }
    let b = B {
        f: &|b| {
            k1.set(k1.get() - 1);
            return a(k1.get(), &|| (b.f)(b), x1, x2, x3, x4);
        },
    };
    let b = || (b.f)(&b);
    return if k <= 0 { x4() + x5() } else { b() };
}

pub fn main() {
    println!("{}", a(10, &|| 1, &|| -1, &|| -1, &|| 1, &|| 0));
}