刚刚看到两句话，感觉不错，分享给大家：

1.用户的问题。就是我们的问题

2.做一些用户想要的东西

(define add1  (lambda (x)    (+ 1 x)))(define sub1  (lambda (x)    (- x 1)))(add1 67)(sub1 5)(sub1 0)(zero? 22)(define addup  (lambda (tup)    (cond      ((null?

tup) 0) (else (+ (car tup) (addup (cdr tup))))))) (addup '(3 4 5)) (define * (lambda (x y) (cond ((eq? 1 x) y) (else (+ y (* (sub1 x) y)))))) (* 3 9) (define tup+ (lambda (tup1 tup2) (cond ((null?

tup1) '()) (else (cons (+ (car tup1) (car tup2)) (tup+ (cdr tup1) (cdr tup2))))))) (tup+ '(2 3 4 5) '(5 4 3 2)) (define > (lambda (x y) (cond ((zero? x) #f) ((zero? y) #t) (else (> (sub1 x) (sub1 y)))))) (> 4 3) (> 3 3) (> 3 4) (define < (lambda (x y) (cond ((zero?

y) #f) ((zero? x) #t) (else (< (sub1 x) (sub1 y)))))) (< 3 3) (< 4 3) (< 3 4) (define = (lambda (x y) (cond ((> x y) #f) ((< x y) #f) (else #t)))) (= 3 4) (= 3 3) (= 4 3) (define expt (lambda (x y) (cond ((zero?

y) 1) (else (* x (expt x (sub1 y))))))) (expt 5 3) (define / (lambda (x y) (cond ((< x y) 0) (else (add1 (/ (- x y) y)))))) (/ 10 2) (define length (lambda (lat) (cond ((null? lat) 0) (else (add1 (length (cdr lat))))))) (length '(good hello)) (define pick (lambda (n lat) (cond ((eq? n 1) (car lat)) (else (pick (sub1 n) (cdr lat)))))) (pick 3 '(hotdogs with hot mustard)) (define no-nums (lambda (list) (cond ((null? list) '()) ((number? (car list)) (no-nums (cdr list))) (else (cons (car list) (no-nums (cdr list))))))) (no-nums '(5 pears 6 prunes 9 dates)) (define all-nums (lambda (lat) (cond ((null? lat) '()) ((number? (car lat)) (cons (car lat) (all-nums (cdr lat)))) (else (all-nums (cdr lat)))))) (all-nums '(99 abc 33 mm 9 gg fuck)) (define eqlat? (lambda (a1 a2) (cond ((and (null? a1) (null? a2)) #t) ((and (number? (car a1)) (number? (car a2))) (cond ((= (car a1) (car a2)) (eqlat?

(cdr a1) (cdr a2))) (else #f))) ((eq?

(car a1) (car a2)) (eqlat?

(cdr a1) (cdr a2))) (else #f)))) (eqlat? '(a b c 33) '(a b c 33)) (define occur (lambda (a lat) (cond ((null? lat) 0) ((number? a) (cond ((and (number? (car lat)) (= (car lat) a)) (add1 (occur a (cdr lat)))) (else (occur a (cdr lat))))) ((number? (car lat)) (occur a (cdr lat))) ((eq?

a (car lat)) (add1 (occur a (cdr lat)))) (else (occur a (cdr lat)))))) (occur 'a '(a b c d e a 3 4 a)) (occur 3 '(b cd e 3 4 3 ed 3)) (define one? (lambda (n) (= n 1))) (one? 3)