PHP: Array 2 JSON

Genial función en PHP que transforma un array PHP en una salida tipo Json. Genial para PHP4 que no integraba esta funcionalidad de serie.

function array2json($arr) {
  if(function_exists('json_encode')) return json_encode($arr); //Lastest versions of PHP already has this functionality.
  $parts = array();
  $is_list = false; 

  //Find out if the given array is a numerical array
  $keys = array_keys($arr);
  $max_length = count($arr)-1;
  if(($keys[0] == 0) and ($keys[$max_length] == $max_length)) {//See if the first key is 0 and last key is length - 1
      $is_list = true;
      for($i=0; $i$value) {
      if(is_array($value)) { //Custom handling for arrays
          if($is_list) $parts[] = array2json($value); /* :RECURSION: */
          else $parts[] = '"' . $key . '":' . array2json($value); /* :RECURSION: */
      } else {
          $str = '';
          if(!$is_list) $str = '"' . $key . '":'; 

          //Custom handling for multiple data types
          if(is_numeric($value)) $str .= $value; //Numbers
          elseif($value === false) $str .= 'false'; //The booleans
          elseif($value === true) $str .= 'true';
          else $str .= '"' . addslashes($value) . '"'; //All other things
          // :TODO: Is there any more datatype we should be in the lookout for? (Object?) 

          $parts[] = $str;
      }
  }
  $json = implode(',',$parts); 

  if($is_list) return '[' . $json . ']';//Return numerical JSON
  return '{' . $json . '}';//Return associative JSON
}