序列操作

看完这一节，感觉世界观又被重塑。
首先说说这一小节的标题”序列作为一种约定的界面”是什么意思:这句话意思是序列作为程序不同模块间数据流动的形式。
学习lisp语言不久，lisp就给了我很多惊喜，我特地新建了一个文件夹叫astonishing来放代码☺
下面是这一节我的代码：

(define nil (list));(define (enumerate-tree-leaves t)  (cond ((null? t) nil)        ((not (pair? t)) (list t))        (else (append (enumerate-tree-leaves (car t))                      (enumerate-tree-leaves (cdr t))))));(define (enumerate-interval low high)  (define (enumerate-iter h ans)    (if (> low h)        ans        (enumerate-iter (- h 1) (cons h ans))))  (enumerate-iter high nil));(define (filter predicate sequence)  (cond ((null? sequence) nil)        ((predicate (car sequence)) (cons (car sequence)                                          (filter predicate (cdr sequence))))        (else (filter predicate (cdr sequence)))));(define (accumulate op initial sequence)  (if (null? sequence)      initial      (op (car sequence) (accumulate op initial (cdr sequence)))));(define (append x y)  (accumulate cons y x));(define (my-map proc sequence)  (accumulate (lambda (x y) (cons (proc x) y)) nil sequence));(define (sum-odd-squares tree)  (accumulate + 0 (map (lambda (x) (* x x))                       (filter (lambda (x) (= (remainder x 2) 1)) (enumerate-tree-leaves t)))));(define (even-fibs n)  (define (fib x)    (define (fib-iter a b k)      (if (= k x)          a          (fib-iter b (+ a b) (+ 1 k))))    (fib-iter 0 1 0))  (filter (lambda (x) (= (remainder x 2) 0))          (map fib (enumerate-interval 0 6))));(define (my-min sequence)  (accumulate (lambda (x y)                       (if (< x y)                           x                           y))              10000              sequence));2.33(define (length sequence)  (accumulate (lambda (x y) (+ 1 y)) 0 sequence));2.34(define (horner-eval x coefficient-sequence)  (accumulate (lambda (a b) (+ a (* x b))) 0 coefficient-sequence))                                        ;2.35(define (count-leaves t)  (accumulate + 0 (map (lambda (x)                         (if (pair? x)                             (count-leaves x)                             1))                       t)));2.36(define (accumulate-n op init seqs)  (if (null? (car seqs))      nil      (cons (accumulate op init                        (map car seqs))            (accumulate-n op init (map cdr seqs)))));2.37(define (dot-product v w)  (accumulate + 0 (map * v w)))(define (matrix-*-vector m v)  (map (lambda (line) (dot-product line v)) m))(define (transpose m)  (accumulate-n cons nil m))(define (matrix-*-matrix m n)  (let ((cols (transpose n)))    (map (lambda (row)           (map (lambda (col)                  (dot-product col row))                cols))         m)));2.38(define (fold-left op init seq)  (define (iter tmp ans)    (if (null? tmp)        ans        (iter (cdr tmp) (op ans (car tmp)))))  (iter seq init));2.39效率为O(n^2)(define (reverse1 sequence)  (accumulate (lambda (x y) (append y (list x))) nil sequence));效率为O(n)(define (reverse2 sequence)  (fold-left (lambda (x y) (cons y x)) nil  sequence))