Happy PI day with Rust !

fn machinpi(dcnt: usize) -> Int {
    fn arccot(x: &Int, unity: &Int) -> Int {
        fn _arccot(x: &Int, n: &Int, xpow: &Int, term: &Int, l: &Int) -> Int {
            let zero = Int::from(0);
            if zero == *term {
                term.to_owned()
            } else {
                let one = Int::from(1);
                let a = partial!(_arccot => x, &(n + 2), &(xpow / x), &(xpow / n), _);
                let b = xpow / n;
                if one == *l {
                    a(&zero) + b
                } else {
                    a(&one) - b
                }
            }
        }
        _arccot(&(x * x), &Int::from(1), &(unity / x), &(unity / x), &Int::from(1))
    }

    let guard = 10 + 10_f32.log10().ceil() as usize;
    let unity = Int::from(10).pow(dcnt + guard);
    let a = 4 * arccot(&Int::from(5), &unity);
    let b = arccot(&Int::from(239), &unity);
    let c = &Int::from(10).pow(guard);
    4 * (a - b) / c
}