fib.php

<?php
/**
 * @return Generator
 */
function fib()
{
    [$a, $b] = [0, 1];
    while (true) {
        yield $b;
        [$a, $b] = [$b, $a + $b];
        if ($b > 10000) {
            return ;
        }
    }
}

foreach (fib() as $item) {
    var_dump($item);
}