Guided Practice 9.2

;; A Queen is a (list PosInt PosInt)

(define (make-queen row col) (list row col))
(define (queen-row q) (first q))
(define (queen-col q) (rest q))

Everything manipulates queens through this interface, so nothing else need change. (For full credit on a homework, you'd need interpretation, template, etc., but this is the idea.)