1 ;; The first three lines of this file were inserted by DrScheme. They record metadata
2 ;; about the language level of this file in a form that our tools can easily process.
3 #reader(lib "htdp-intermediate-reader.ss" "lang")((modname 18.1.8) (read-case-sensitive #t) (teachpacks ((lib "draw.ss" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "draw.ss" "teachpack" "htdp")))))
4 (define MRPOLY (list (make-posn 20 30)
5                      (make-posn 30 40)
6                      (make-posn 50 90)
7                      (make-posn 100 40)
8                      (make-posn 150 80)
9                      (make-posn 240 120)
10                      (make-posn 40 10)))
11 
12 (define (modified-draw-polygon a-poly)
13   (local ((define (draw-polygon a-poly)
14             (cond
15               [(empty? (rest a-poly)) true]
16               [else (connect-dots (cons (last a-poly) a-poly))]))
17           
18           (define (connect-dots a-poly)
19             (cond
20               [(empty? (rest a-poly)) true]
21               [else (and
22                      (draw-solid-line (first a-poly)
23                                       (second a-poly)
24                                       'black)
25                      (connect-dots (rest a-poly)))]))
26           
27           (define (last a-poly)
28             (cond
29               [(empty? (rest a-poly)) (first a-poly)]
30               [else (last (rest a-poly))]))
31           (define (add-at-end a-poly first-posn)
32             (cond
33               [(empty? (rest a-poly)) (first a-poly)]
34               [else (cons (add-at-end a-poly first-posn) (cons first-posn empty))]))
35           (define (modified-draw-polygon a-poly)
36             (cond
37               [(empty? (rest a-poly)) true]
38               [else (connect-dots (add-at-end a-poly (first a-poly)))])))
39     (modified-draw-polygon a-poly)))
40 
41 (start 500 500)
42 (modified-draw-polygon MRPOLY)