Windows Page Number Expansion

get_pages.php

<?php

    $pages = '3,5,8-12,15,16,20-22';
    #remove all whitespace
    #validate format
    
    $page_list = explode(',', $pages);
    
    $page_expander = function($element) {
        $pages = explode('-', $element);
        if (count($pages) == 1) {
            return $pages;
        }
        
        return range($pages[0], $pages[1]);
    };
    
    $page_list = call_user_func_array('array_merge', array_map($page_expander, $page_list));

    print_r($page_list);