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-beginner-reader.ss" "lang")((modname 11.3.3) (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 ;;Produces an intenger between n and m-1
5 
6 ;; random-n-m : integer integer  ->  integer
7 ;; ... 
8 ;; Assume: n < m
9 (define (random-n-m n m)
10   (+ (random (- m n)) n))
11 ;
12 ;create-temps : number number number -> list-of-numbers
13 ;Creates a list-of-numbers consisting of n numbers between low and high.
14 ;Example
15 ;(create-temps 0 low high)
16 ;empty
17 ;(create-temps 1 low high)
18 ;(cons (random-n-m low (+ high 1)) empty)
19 ;(create-temps 2 low high)
20 ;(cons (random-n-m low (+ high 1)) (cons (random-n-m low (+ high 1)) empty))
21 ;
22 ;Template
23 ;
24 ;(define (create-temps n low high)
25 ;  (cond
26 ;    [(zero? n) ...]
27 ;    [(>= n 1) ...]
28 ;    [else (error 'create-temps "expected 1st arg: natural number")]))
29 
30 (define (create-temps n low high)
31   (cond
32     [(zero? n) empty]
33     [(>= n 1) (cons (random-n-m low (+ high 1)) (create-temps (sub1 n) low high))]
34     [else (error 'create-temps "expected 1st arg: natural number")]))
35 
36 ;Data Definition
37 ;A list-of-temperatures is either
38 ;1. an empty list or
39 ;2. (cons t los) where t is a number and los is a list-of-temperatures.
40 
41 ;Header, Purpose, Contract
42 ;check-range1? : list-of-temperatures -> boolean
43 ;Given a-list, returns true if the list of temperatures are within the range
44 ;low and high (endpoints included as true).
45 ;
46 (define (check-range1? a-list low high)
47   (cond
48     [(empty? a-list) true]
49     [(cons? a-list) (cond
50                      [(and
51                        (number? (first a-list))
52                        (>= (first a-list) low)
53                        (<= (first a-list) high))
54                       (check-range1? (rest a-list) low high)]
55                      [(number? (first a-list)) false]
56                      [else
57                       (error 'check-range1? "list should be composed of numbers")])]
58     [else (error 'check-range1? "expected 3 arg: list number number")]))
59 
60 ;create-prices : natural-number number number -> list-of-numbers
61 ;Given a natural-number n, creates a list of n prices
62 ;between low and high rounded to the nearest
63 ;dime ($0.10).  Creates this list by
64 ;making the function call random-dime.
65 ;
66 ;Examples
67 ;(create-prices 0 low high)
68 ;empty
69 ;(create-prices 1 low high)
70 ;(cons (random-dime low high) empty)
71 ;(create-prices 2 low high)
72 ;(cons (random-dime low high)
73 ;      (cons (random-dime low high) empty))
74 ;
75 (define (create-prices n low high)
76   (cond
77     [(zero? n) empty]
78     [(>= n 1) (cons (random-dime low high) (create-prices (sub1 n) low high))]
79     [else (error 'create-prices "expected 1st arg: natural-number")]))
80 
81 ;random-dime : number number -> number
82 ;Given low and high, creates a number (decimal) between low and high
83 ;rounded to the nearest dime.  It does so by choosing a random integer
84 ;between 0 and (high-low)/0.1, inclusive.  So for example,
85 ;for low=0 and high=1, it chooses a number between 0 and 10 (inclusive).
86 ;It then multiplies this number by 0.1, the value of a dime.
87 ;This function thus returns us a number between $0.00 and $1.00,
88 ;rounded to the nearest dime.
89 
90 (define (random-dime low high)
91   (*
92    (random-n-m 0
93                (+ (/ (- high low) 0.1) 1))
94    0.1))
95 
96 ;
97 ;dollar-store? : list-of-numbers -> boolean
98 ;Checks a-list to see if the prices are below 1. Returns true
99 ;if the statement is true, false otherwise.
100 ;
101 ;Template
102 ;(define (dollar-store? a-list)
103 ;  (cond
104 ;    [(empty? a-list) ...]
105 ;    [(cons? a-list) (first a-list) (rest a-list)]))
106 
107 (define (dollar-store? a-list)
108   (cond
109     [(empty? a-list) true]
110     [(cons? a-list) (cond
111                       [(and
112                         (number? (first a-list))
113                         (< (first a-list) 1))
114                        (dollar-store? (rest a-list))]
115                       [else false])]))
116 
117 ;eval-until-true : natural-number number number -> boolean
118 ;Keep evaluating (dollar-store? (create-prices n low high))
119 ;until it returns true.
120 ;
121 (define (eval-until-true n low high)
122   (cond
123     [(dollar-store? (create-prices n low high)) true]
124     [else (eval-until-true n low high)]))