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-lambda-reader.ss" "lang")((modname |27.2|) (read-case-sensitive #t) (teachpacks ((lib "draw.ss" "teachpack" "htdp") (lib "arrow.ss" "teachpack" "htdp") (lib "gui.ss" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "draw.ss" "teachpack" "htdp") (lib "arrow.ss" "teachpack" "htdp") (lib "gui.ss" "teachpack" "htdp")))))
4 ;create-matrix : N (listof numbers) -> (listof (listof numbers))
5 ;Given n (N[>=1]) and alon (alon has a length of n by m, where m is any integer), return a (listof (listof numbers)) representing an n by m matrix.
6 
7 (define (create-matrix n alon)
8   (cond
9     [(empty? alon) empty]
10     [(zero? n) (error 'create-matrix "expected arg: nonzero number")]
11     [(not (= (remainder (length alon) n) 0)) (error 'create-matrix "improper dimensions")]
12     [else (cons (first-n n alon)
13                 (create-matrix n (remove-n n alon)))]))
14 
15 ;first-n : N (listof numbers) -> (listof numbers)
16 ;Returns the first n numbers of alon as a (listof numbers).
17 
18 (define (first-n n alon)
19   (cond
20     [(zero? n) empty]
21     [else (cons (first alon)
22                 (first-n (sub1 n) (rest alon)))]))
23 
24 ;remove-n : N (listof numbers) -> (listof numbers)
25 ;Removes the first n numbers of alon and returns the result as a (listof numbers).
26 
27 (define (remove-n n alon)
28   (cond
29     [(zero? n) alon]
30     [else (remove-n (sub1 n) (rest alon))]))
31 
32 (equal? (create-matrix 2 '(4 5 6 7 8 9)) '((4 5)
33                                            (6 7)
34                                            (8 9)))
35 (create-matrix 3 '(4 5 6 7 8 9))