Lazy Fibonacci generator in Rust

fibonacci.rs

use std::iter::Unfold;

fn main() {
  let it = fibonacci();

  // prints the sequence
  //for i in it.take(10) {
  //  print!("{} ", i)
  //}

  // doesn't print anything
  it.take(10).inspect(|&i| {
    print!("{} ", i)
  });

  println!("")
}

fn fibonacci() -> Unfold<uint, FibState> {
  let st = FibState{curr: 1, next: 2};
  Unfold::new(st, fib_next)
}

struct FibState {
  curr: uint,
  next: uint
}

fn fib_next(st: &mut FibState) -> Option<uint> {
  let prev = st.curr;
  st.curr = st.next;
  st.next = prev + st.next;
  Some (prev)
}