How to traverse an infinite array with a return

How do I iterate through an infinite array with a return?
$arr =array (Array (6,66), 8);
function Arr_p ($arr) {
foreach ($arr as $v) {
if (Is_array ($v)) {
Arr_p ($v);
}else{
echo $v. "
";}
}
}
Arr_p ($arr);
?>

This paragraph is the direct echo out, now want to use return, do not know how to start, I hope the expert pointing! (younger brother is PHP beginner)

------Solution--------------------
$arr =array (Array (6,66), 8);
function Arr_p ($arr) {
$r = ";
foreach ($arr as $v) {
if (Is_array ($v)) {
$r. = Arr_p ($v);
}else{
$r. = $v. "
";}
}
return $r;
}
echo arr_p ($arr);
------Solution--------------------

PHP Code

function Arr_p ($arr) {  $r = ';//Because you want to return data, there is a carrier  foreach ($arr as $v) {    if (Is_array ($v)) {///If it is an array, it is recursively entered      $r. = Arr_p ($v);//Catch the returned data    } else{      $r. = $v. "
"; Not an array, do you want to save the data?}  return $r;//Return Data}
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