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 19.1.4) (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 (squared>? x c)
5   (> (* x x) c))
6 
7 ;filter : predicate list-of-numbers
8 ;Filters out all numbers in a-lon where the predicate of the number evaluates to false.  Retains all numbers that evaluate to true.
9 (define (filter1 predicate a-lon t)
10   (cond
11     [(empty? a-lon) empty]
12     [(predicate (first a-lon) t) (cons (first a-lon)
13                                        (filter1 predicate (rest a-lon) t))]
14     [else (filter1 predicate (rest a-lon) t)]))
15 
16 #|
17 (filter1 squared>? (list 4 5) 10)
18 = (cons 4 (filter1 squared>? (list 5) 10))
19 
20 (cond
21   [(empty? (list 4 5)) empty]
22   [(squared>? (first (list 4 5)) 10) (cons (first (list 4 5))
23                                           (filter1 squared>? (rest (list 4 5)) 10))]
24   [else (filter squared>? (rest (list 4 5)))])
25 
26 (cond
27   [false empty]
28   [true (cons 4
29               (filter1 squared>? (list 5) 10))]
30   [else (filter squared>? (rest (list 4 5)))])
31 
32 (cons 4 (filter1 squared>? (list 5) 10))
33 |#
34 
35 ;below : list-of-numbers number -> list-of-numbers
36 ;Given a-lon, return all numbers below a-number as a list-of-numbers.
37 
38 (define (below a-lon a-number)
39   (filter1 < a-lon a-number))
40 
41 ;above: list-of-numbers number -> list-of-numbers
42 ;Given a-lon, return all numbers above a-number as a list-of-numbers.
43 
44 (define (above a-lon a-number)
45   (filter1 > a-lon a-number))