<?php
class board_game {
    function move_next() {
        echo "next\n";
    }

    function move_prev() {
        echo "prev\n";
    }
}

interface price {
    function get_price();
}

class monopoly 
    extends board_game 
    implements price 
{
    function get_price() {
        return 22.95;
    }
}

$g = new monopoly;
if ($g instanceof price) {
    var_dump($g->get_price());
}

?>