Find first occurrence of key in PHP array

find.php

<?php
$test_arr = array(
    "a" => array(
        "aa" => 0,
        "ab" => 1
    ),
    "b" => array(
        "ba" => array(
            "baa" => 3,
            "bab" => 4
        )
    )
);

$to_find = "bab";
$result = find_key($test_arr, $to_find);

var_dump($result);
// int(4)

function find_key($arr, $key_name) {
    foreach ($arr as $key => $value) {
        if ("$key" == $key_name) {
            return $value;
        }

        if (gettype($value) == "array") {
            $r = find_key($value, $key_name);

            if ( $r )
                return $r;
        }
    }

    return NULL;
}
?>