calculates the greatest-common-divisor of many argv `i128`s using Euclidean algorithm

variadic GCD simple CLI.rs

/// # Greatest Common Divisor / Highest Common Factor
/// between `a` & `b`,
/// using https://en.wikipedia.org/wiki/Euclidean_algorithm.
///
/// It only supports unsigneds,
/// because it's easier to avoid bugs,
/// and allows wider input ranges.
const fn gcd(mut a: u128, mut b: u128) -> u128 {
	// rustc doesn't have TCO, so recursion is not an option
	while b != 0 {
		// we could use tuple literals, instead of array literals,
		// but arrays are "more type safe", because of homogeneity
		[a, b] = [b, a % b];
		// this destructuring asignment allows us to get the beauty of recursion
		// with imperative programming!
	}
	a
}

fn main() {
	println!(
		"{}",
		std::env::args()
			.skip(1)
			.map(|s| s.parse::<i128>().unwrap().unsigned_abs())
			.reduce(gcd)
			.unwrap_or(0) // GCD identity: gcd(x, 0) = x
	);
}