SICP 1.29-1.33

1.29

 (define (sum term a next b)
   (if (> a b)

       (+ (term a)
          (sum term (next a) next b))))

 (define (cube x)
   (* x x x))

 (define (integral f a b n)
   (define (helper f a b n k)
     (define (next k)
       (+ a (* k (/ (- b a) n))))
     (cond ((= k n) (f (next k)))
           ((= k ) (+ (f (next k))
                       (helper f a b n )))
           ((= (remainder k ) ) (+ (*  (f (next k)))
                                     (helper f a b n (+ k ))))
           (else (+ (*  (f (next k)))
                    (helper f a b n (+ k ))))))
   (/ (* (helper f a b n ) (/ (- b a) n)) ))

 ----- 出现 xxxx is not applicable 的错误, 有可能是由于把函数写成了中缀表达式的情况.

1.30

 (define (sum term a next b)
   (define (iter a result)
     (if (= a b)
         result
         (iter (next a) (+ result
                           (term a)))))
   (iter a ))

1.31

---> 没必要写,和前面差不多

1.32

 (define (accumulate combiner null-value term a next b)
   (if (> a b)
       null-value
       (combiner (term a)
                 (accumulate combiner null-value term (next a) next b))))

1.33

----> 类似 不写了就...