;
2.2
(define (make-
point x y)
(cons x y))
(define (x-
point p)
(car p))
(define (y-
point p)
(cdr p))
(define (print-
point p)
(newline)
(display "{")
(display (x-
point p))
(display ",")
(display (y-
point p))
(display "}"))
(define (make-segment start-segment end-
segment)
(cons start-
segment
end-
segment))
(define (start-
segment l)
(car l))
(define (end-
segment l)
(cdr l))
(define (average x y)
(/ (+
x y)
2))
(define (midpoint-
segment l)
(let ((start (start-
segment l))
(end (end-
segment l)))
(make-point (average (x-
point start)
(x-
point end))
(average (y-
point start)
(y-
point end)))))
(print-point (make-point
1 1))
(define start (make-point
1 3))
(define end (make-point
4 3))
(define seg (make-
segment start end))
(define mid (midpoint-
segment seg))
(print-
point mid)
(define (perimeter-
rectangle sq)
(let ((length (length-of-
rectangle sq))
(width (width-of-
rectangle sq)))
(*
2
(+
length width))))
(define (area-
rectangle sq)
(* (length-of-
rectangle sq)
(width-of-
rectangle sq)))
;
(define (make-rectangle length-
1 length-
2 width-
1 width-
2)
(cons (cons length-
1 length-
2)
(cons width-
1 width-
2)))
;; selector
(define (length-
1-
rectangle r)
(car (car r)))
(define (length-
2-
rectangle r)
(cdr (car r)))
(define (width-
1-
rectangle r)
(car (cdr r)))
(define (width-
2-
rectangle r)
(cdr (cdr r)))
转载于:https://www.cnblogs.com/R4mble/p/8395202.html
