1 12687dd9 2023-08-04 jrmu ;; The first three lines of this file were inserted by DrScheme. They record metadata
 2 12687dd9 2023-08-04 jrmu ;; about the language level of this file in a form that our tools can easily process.
 3 12687dd9 2023-08-04 jrmu #reader(lib "htdp-intermediate-reader.ss" "lang")((modname |22.2|) (read-case-sensitive #t) (teachpacks ((lib "draw.ss" "teachpack" "htdp") (lib "arrow.ss" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "draw.ss" "teachpack" "htdp") (lib "arrow.ss" "teachpack" "htdp")))))
 4 12687dd9 2023-08-04 jrmu Exercise 22.2.2.   Define an abstract version of sort (see exercise 19.1.6) using the new recipe for abstraction.    Solution
 5 12687dd9 2023-08-04 jrmu 
 6 12687dd9 2023-08-04 jrmu ;; sort : list-of-numbers predicate ->  list-of-numbers
 7 12687dd9 2023-08-04 jrmu ;; to construct a list with all items from alon in ascending or descending order
 8 12687dd9 2023-08-04 jrmu (define (sort1 alon predicate)
 9 12687dd9 2023-08-04 jrmu   (local ((define (sort alon)
10 12687dd9 2023-08-04 jrmu 	    (cond
11 12687dd9 2023-08-04 jrmu 	      [(empty? alon) empty]
12 12687dd9 2023-08-04 jrmu 	      [else (insert (first alon) (sort (rest alon)))]))
13 12687dd9 2023-08-04 jrmu 	  (define (insert an alon)
14 12687dd9 2023-08-04 jrmu 	    (cond
15 12687dd9 2023-08-04 jrmu 	      [(empty? alon) (list an)]
16 12687dd9 2023-08-04 jrmu 	      [else (cond
17 12687dd9 2023-08-04 jrmu 		      [(predicate an (first alon)) (cons an alon)]
18 12687dd9 2023-08-04 jrmu 		      [else (cons (first alon) (insert an (rest alon)))])])))
19 12687dd9 2023-08-04 jrmu     (sort alon)))
20 12687dd9 2023-08-04 jrmu 
21 12687dd9 2023-08-04 jrmu ;sort-ascend : list-of-numbers
22 12687dd9 2023-08-04 jrmu ;Given a-lon, return a list-of-numbers sorted in ascending order.
23 12687dd9 2023-08-04 jrmu (define (sort-ascend alon)
24 12687dd9 2023-08-04 jrmu   (sort1 alon <))
25 12687dd9 2023-08-04 jrmu 
26 12687dd9 2023-08-04 jrmu ;sort-descend : list-of-numbers
27 12687dd9 2023-08-04 jrmu ;Given a-lon, return a list-of-numbers sorted in descending order.
28 12687dd9 2023-08-04 jrmu (define (sort-ascend alon)
29 12687dd9 2023-08-04 jrmu   (sort1 alon >))
30 12687dd9 2023-08-04 jrmu 
31 12687dd9 2023-08-04 jrmu ;; sort : list-of-numbers  ->  list-of-numbers
32 12687dd9 2023-08-04 jrmu ;; to construct a list with all items from alon in descending order
33 12687dd9 2023-08-04 jrmu (define (sort alon)
34 12687dd9 2023-08-04 jrmu   (local ((define (sort alon)
35 12687dd9 2023-08-04 jrmu 	    (cond
36 12687dd9 2023-08-04 jrmu 	      [(empty? alon) empty]
37 12687dd9 2023-08-04 jrmu 	      [else (insert (first alon) (sort (rest alon)))]))
38 12687dd9 2023-08-04 jrmu 	  (define (insert an alon)
39 12687dd9 2023-08-04 jrmu 	    (cond
40 12687dd9 2023-08-04 jrmu 	      [(empty? alon) (list an)]
41 12687dd9 2023-08-04 jrmu 	      [else (cond
42 12687dd9 2023-08-04 jrmu 		      [(> an (first alon)) (cons an alon)]
43 12687dd9 2023-08-04 jrmu 		      [else (cons (first alon) (insert an (rest alon)))])])))
44 12687dd9 2023-08-04 jrmu     (sort alon)))