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run code in 300+ PHP versions simultaneously
<?php $pattern="\( ( (?>[^()]+) | (?R) )* \)"; $str="(def a (x) (+ 1 x))(print (a 1))"; preg_match_all($pattern,$str,$out); var_dump($out);

preferences:
36.98 ms | 402 KiB | 5 Q