Calling PHP in BBCode

[Gargi]

I want to parse some php code using a bbcode tag. Maybe another example with options:

Tag: count
Parameter a Name, Option a number.
e.g: [count="3"]Gargi[/count]

While parsing the number should be added to another value. Output maybe:

Hello this is Gargi,
my number is 10

So I try it with a plugin bbcode_fetch_tags:

PHP Code:

$tag_list['option']['count'] = array(  
    'callback' => 'handle_external', 
    'external_callback' => 'handle_bbcode_count_callback',  
    'strip_empty' => true  
);  
   
if(!function_exists('handle_bbcode_count_callback'))  
{  
    function handle_bbcode_count_callback(&$parsed, $value, $option)  
    {  
          $result = 7 + $option;
          return "Hello this is ".$value.",<br />";
          return "my number is ".$result;
          return $parsed;

    }  
} 


This will just result in

Hello this is Gargi,

and nothing more. I also only added this plugin and nothing more. Is there anything else to do for it (another plugin) or where do I have to place the php code to be executed correctly?

cu
Gargi