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run code in 300+ PHP versions simultaneously
<?php function is_intstr($val) { return preg_match("/^(0|[1-9][0-9]*)$/", $val); } foreach(range(0, 10) as $n) { echo $n; echo " - "; echo is_intstr($n); echo "\n"; }

preferences:
40.99 ms | 402 KiB | 5 Q