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 |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 ;Exercise 22.2.1.   Define an abstraction of the functions convertCF and names from section 21.1 using the new recipe for abstraction.    Solution
5 
6 (define-struct ir (name price))
7 
8 ;An inventory record (ir) is a structure
9 ;(make-ir name price)
10 
11 #|
12 
13 ;; convertCF : lon  ->  lon
14 (define (convertCF alon)
15   (cond
16     [(empty? alon) empty]
17     [else
18      (cons (operator (first alon))
19            (convertCF (rest alon)))]))
20 
21 ;; names : (listof ir)  ->  los
22 (define (names aloir)
23   (cond
24     [(empty? aloir) empty]
25     [else
26      (cons (operator (first aloir))
27            (names (rest aloir)))]))
28 
29 |#
30 
31 ;abs-func : (X -> Y) -> ((listof X) -> (listof Y))
32 (define (abs-map operator)
33   (local ((define (map alox)
34             (cond
35               [(empty? alox) empty]
36               [else (cons (operator (first alox))
37                           (map (rest alox)))])))
38     map))
39 
40 ;C->F : number -> number
41 (define (C->F temp)
42   (+ (* 9/5 temp) 32))
43 
44 (define convertCF (abs-map C->F))
45 (define names (abs-map ir-name))
46 
47 (define listofir (list (make-ir 'Pencil 0.40)
48                        (make-ir 'Eraser 1.99)
49                        (make-ir 'Pen 1.25)
50                        (make-ir 'PaperClip 0.05)
51                        (make-ir 'Highlighter 4.50)))