taneb2.rs

use std::iter::Unfold;

fn main() {
    for fib in next.unfold((0,1)).take(20) {
        println!("{}", fib);
    };
}

fn next(arg: &mut (int, int)) -> Option<int> {
    let (lo, hi) = *arg;
    *arg = (hi, lo + hi);
    Some(lo)
}

trait SillyUnfold<'a, A, St> {
    fn unfold(self, initial_state: St) -> Unfold<'a, A, St>;
}

impl<'a, A, St> SillyUnfold<'a, A, St> for fn<'a>(&mut St) -> Option<A> {
    fn unfold(self, initial_state: St) -> Unfold<'a, A, St> {
        Unfold::new(initial_state, self)
    }
}