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 19.1.0) (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 (filter1 rel-op alon t)
5   (cond
6     [(empty? alon) empty]
7     [else (cond
8             [(rel-op (first alon) t) 
9              (cons (first alon)
10                    (filter1 rel-op (rest alon) t))]
11             [else
12              (filter1 rel-op (rest alon) t)])]))
13 
14 (filter1 < (cons 6 (cons 4 empty)) 5)
15 
16 (cond
17   [false empty]
18   [else (cond
19           [false 
20            (cons (first (cons 6 (cons 4 empty)))
21                  (filter1 rel-op (rest (cons 6 (cons 4 empty))) 5))]
22           [else
23            (filter1 < (rest (cons 6 (cons 4 empty))) 5)])])
24 
25 (filter1 < (rest (cons 6 (cons 4 empty))) 5)
26 
27 (cond
28   [false empty]
29   [else (cond
30           [true 
31            (cons (first (cons 4 empty))
32                  (filter1 rel-op (rest (cons 4 empty)) 5))]
33           [else
34            (filter1 < (rest (cons 4 empty)) 5)])])
35 
36 (cons (first (cons 4 empty))
37       (filter1 rel-op (rest (cons 4 empty)) 5))
38 
39 (cons 4 (filter1 rel-op (rest (cons 4 empty)) 5))
40 
41 (cons 4 (filter1 < empty) 5)
42 (cons 4 empty)
43 
44 (filter1 > (cons 8 (cons 6 (cons 4 empty))) 5)
45 
46 (cond
47   [(empty? alon) empty]
48   [else (cond
49           [(rel-op (first alon) t) 
50            (cons (first alon)
51                  (filter1 rel-op (rest alon) t))]
52           [else
53            (filter1 rel-op (rest alon) t)])])
54 
55 (cons 8 (filter1 > (cons 6 (cons 4 empty)) 5))
56 (cons 8 (cons 6 (filter1 > (cons 4 empty) 5)))
57 (cons 8 (cons 6 (filter1 > empty 5)))
58 (cons 8 (cons 6 empty))