96 lines
2.1 KiB
Markdown
96 lines
2.1 KiB
Markdown
+++
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title = "SICP 第一课"
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author = ["SouthFox"]
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date = 2022-09-02T22:17:00+08:00
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lastmod = 2022-09-02T22:42:53+08:00
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tags = ["publish"]
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draft = false
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+++
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## 程序设计中要思考的问题是？ {#程序设计中要思考的问题是}
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- 程序是抽象的，不像电气设计中的考虑串联几千个放大器（因为要考虑误差等），程序设计是理想化的，可以考率不断循环下对于程序和设计有什么影响。
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## 程序设计的三大想法？ {#程序设计的三大想法}
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- 黑盒抽象
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将简单的部分组合一个部件然后像积木一样不断堆积，这个部件对于外部是抽象的，可以拿来直接用的。
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- 约定接口
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- 元语言抽象
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## Lisp 基础 <span class="tag"><span class="NODE">NODE</span></span> {#lisp-基础}
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### 括号 {#括号}
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Lisp 用括号来表达一个组合式，括号多的时候可以用缩进来减少对身心的损耗（
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### 前缀 {#前缀}
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Lisp 是前缀表达语言，如：
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```scheme
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(+ 1 2)
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```
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结果显示为 3 。
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```text
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3
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```
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### 定义 {#定义}
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用 DEFINE 关键词来定义一个过程（也叫 lambda），通过一些基本过程搭建的过程来完成一个复杂的目的，这就是黑盒。
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例子：求平方根
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```scheme
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(define (square-iter guess x)
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(if (good-enough? guess x)
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guess
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(begin ; used this compound procedure in order to be able to
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(display guess) ; display the intermediate guess values
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(newline)
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(square-iter (improve guess x) x)
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)
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)
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)
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(define (improve guess x)
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(average guess (/ x guess)))
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(define (average x y)
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(/ (+ x y) 2))
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(define (square x)
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(* x x))
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(define (good-enough? guess x)
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(< (abs (- (square guess) x)) 0.001))
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(define (sqrt x)
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(square-iter 1.0 x))
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(define (square-iter-delta guess x)
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(if (in-delta? guess (improve guess x))
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guess
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(begin
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(display guess)
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(newline)
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(square-iter-delta (improve guess x) x)
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)
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)
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)
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(define (in-delta? guess1 guess2)
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(< (abs (- guess1 guess2)) 0.001))
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(define (sqrt-delta x)
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(square-iter-delta 1.0 x))
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(sqrt-delta 25)
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```
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