Ugly solution to this: https://atilanevesoncode.wordpress.com/2018/12/31/comparing-pythagorean-triples-in-c-d-and-rust/

ugly_triples.rs

fn triples() -> impl Iterator<Item=(u32, u32, u32)> {
    let (mut x, mut y, mut z) = (1, 1, 1);
    (0..).map(move |_| {
        loop {
            y += 1;
            if y > z {
                x += 1;
                y = x;
            }
            if x > z {
                z += 1;
                x = 1;
                y = 1;
            }
            if x*x + y*y == z*z {
                return (x, y, z);
            }
        }
    })
}

fn main() {
    for (x, y, z) in triples().take(1000) {
        println!("({}, {}, {})", x, y, z);
    }
}