基本过程：
1 (cons n d) 2 (car x) 3 (cdr x)
部分习题：
exercise 2.1
1 (define (make-rat n d) 2 (let ((g (gcd n d))) 3 (if (negative? (* n d)) 4 (cons (- (abs (/ n g))) (abs (/ d g))) 5 (cons (abs (/ n g)) (abs (/ d g))))))
exercise 2.2
1 (define (average x y) 2 (/ (+ x y) 2)) 3 (define (make-point x y) 4 (cons x y)) 5 (define (x-point p) 6 (car p)) 7 (define (x-point p) 8 (cdr p)) 9 (define (make-segment start end) 10 (cons start end)) 11 (define (start-segment segment) 12 (car segment)) 13 (define (end-segment segment) 14 (cdr segment)) 15 16 (define (midpoint-segment segment) 17 (let ((start-point (start-segment segment)) 18 (end-point (end-segment segment))) 19 (cons (average (x-point start-point) (x-point end-point)) 20 (average (y-point start-point) (y-point end-point)))))
exercise 2.4
1 (define (cdr z) 2 (z (lambda (p q) q))) 3 4 ;代换模型 5 (cdr (cons x y)) 6 7 ((lambda (m) (m x y)) 8 (lambda (p q) q)) 9 10 ((lambda (p q) q) 11 (x y)) 12 13 y
exercise 2.5
1 (define (cons x y) 2 (define (dispatch m) 3 (cond ((= m 0) x) 4 ((= m 1) y) 5 (else (* (expt 2 x) (expt 3 y))))) 6 (dispatch)) 7 (define (car z) (z 0)) 8 (define (cdr z) (z 1))
exercise 2.7
假定 make-interval 的两个参数由小到大排列。
1 (define (upper-bound interval) 2 (cdr interval)) 3 (define (lower-bound interval) 4 (car interval))
exercise 2.8
1 (define (sub-interval x y) 2 (let ((xl (lower-bound x)) 3 (xu (upper-bound x)) 4 (yl (lower-bound y)) 5 (yu (upper-bound y))) 6 (make-interval (- (min xl yl) (max xl yl)) 7 (- (max xu yu) (min xu yu)))))
