primes.php

<?php

/**
 * Run this code with: php -n to make sure no configuration will be used
 * so xdebug will not be used either.
 */

declare(strict_types=1);

function llist($n = 2) {
    yield $n;
    return yield from llist($n + 1);
}

$callback = fn(int $p) => fn(int $a, int $b, Iterator $it): bool => $a % $p !== 0;

$i = 0;
$iterator = llist();
while (true) {
    $prime = $iterator->current();

    var_dump($prime);

    if ($i++ > 100) {
        break;
    }

    $iterator = new CallbackFilterIterator(
        $iterator,
        $callback($prime)
    );

    $iterator->next();
}