Print your name with y combinator

main.rs

// to run: rustc -C opt-level=3 main.rs && ./main

trait YF<T, U> {
    fn apply(&self, yf: &dyn YF<T, U>, u: T) -> U;
}

impl<T, U, F> YF<T, U> for F
where
    F: Fn(&dyn YF<T, U>, T) -> U,
{
    fn apply(&self, yf: &dyn YF<T, U>, t: T) -> U {
        self(yf, t)
    }
}

fn y<T, U>(f: impl Fn(&dyn Fn(T) -> U, T) -> U) -> impl Fn(T) -> U {
    move |n| {
        (&|yf: &dyn YF<T, U>, x| yf.apply(yf, x))(
            &|yf: &dyn YF<T, U>, x| f(&|z| yf.apply(yf, z), x),
            n,
        )
    }
}

fn print_name(name: &str, n: i32) {
    let print = |f: &dyn Fn(i32) -> (), t| {
        if t > 0 {
            println!("{name}");
            f(t - 1)
        }
    };
    y(print)(n)
}

fn main() {
    let name = "fathir";
    let n = 100;
    print_name(name, n);
}