Recursive function to iterate over combinations of an array?

Question

PHP

How to write a recursive function for the below code?

$arr = array('a', 'b', 'c');
$lim = count($arr); 

for($i1 = 0; $i1 < $lim; $i1++) { 
    for($i2 = 0; $i2 < $lim; $i2++) { 
        for($i3 = 0; $i3 < $lim; $i3++) { 
       echo $arr[$i1].$arr[$i2].$arr[$i3].'<br>';
        } 
    } 
}

Answer 1

www.stackoverflow.com/a/15902836

Answer 2

stackoverflow.com/a/19067884
From above link
Replace with
$output = sampling($chars, count($chars));