Cartesian in PHP

cartesian.php

function cartesian($input) {
  //get cartesian product (permutations) of a nested array
  /* x = [
   *   a = [1,2],
   *   b = [10,20,30]
   * ]
   * returns [ [1,10] , [1,20] , [1,30] , [2,10], [2,20], [2,30] ]
   */
  $result = array(array());
  
  foreach ($input as $k => $v) {
    $permut = array();
    foreach($result as $product){
      foreach($v as $item) {
        $product[$k] = $item;
        $permut[] = $product;
      }
    }
    
    $result = $permut;
  }
  
  return $result;