Backwards while loop.

while-dec.rs

use std;
import std::vec;

fn main() {
  auto v = [1, 2];
  auto i = vec::len[int](v) - 1u;
  while (i != 0u) {
    log_err i;
    log_err v.(i);
    i -= 1u;
  }
  assert i == 0u;
}