第十六章 反复精化设计
最后更新于：2022-04-02 04:14:34
[TOC]
## 概述
## 16.2.1
把图 16.1 中的文件系统转化为 Scheme 表示
```
(define dir (list (list 'part1 'part2 'part3) (list (list (list 'hang 'draw) (list 'read!))) 'read!))
```
## 16.2.2
开发函数 how-many，该函数读入一个 dir，返回该 dir 树中的文件数
```
(define (how-many dir)
(cond
[(empty? dir) 0]
[(symbol? (first dir)) (+ 1 (how-many (rest dir)))]
[else (+ (how-many (first dir)) (how-many (rest dir)))]))
(define dir (list (list 'part1 'part2 'part3) (list (list (list 'hang 'draw) (list 'read!))) 'read!))
(how-many dir) ;7
```
## 16.3.2
习题 16.3.2 开发函数 how-many，该函数读入一个（依照模型三的）dir，返回该 dir 树中的文件数。
```
(define-struct file (name size content))
(define-struct dir (name dirs files))
;; 定义目录树
(define dir-list (make-dir 'ts
(list
(make-dir 'Text empty (list
(make-file 'part1 99 empty)
(make-file 'part2 52 empty)
(make-file 'part3 17 empty)))
(make-dir 'Libs (list
(make-dir 'Code empty
(list
(make-file 'hand 8 empty)
(make-file 'draw 2 empty)))
(make-dir 'Docs empty (list (make-file 'read! 19 empty))))
empty))
(list (make-file 'read! 10 empty))
))
```
';