SICP Learning Notes

当我们考察一门语言时，主要看三点

primitives：元操作是什么
means of combinations：如何组合
means of abstraction：如何抽象，构造更复杂的程序

数据和过程之间没有本质的区别

在写完构造器（constrcutor）之后，记得写上选择器（selector）。

+---------+       rule          +--------+
| pattern +-------------------->+skeleton|
+----+----+                     +----+---+
     |                               |
     |                               |
     |match                          |instantiation
     |                               |
     v                               v
+----+-----+                    +----+-----+
|expression|                    |expression|
|  source  +------------------->+  target  |
+----------+                    +----------+

pattern match

foo – matches exactly foo (f a b) – matches a list, whose first element is f, etc. (? x) – matches anything, call it x (?c x) – matches a constant, call it x (?v x) – matches a variable, call it x

skeletons

foo – instantiates to itself (f a b) – instantiates to a 3-list, results of instatiating each of f, a, b (: x) – instatantiates to the value of x in the pattern matched

任何一个复杂的大程序都是由简单的小部分组成。纵然递归模式非常复杂，最重要的事情就是：不去思考它。如果取思考它的实际行为，大家就会迷惑。

Convince yourself something is right.

好的编程或设计方法就是你知道什么不用去思考！

Wishful thinking is crucial!

Lisp 没有循环，靠递归的 procedure 实现迭代，这并不表示 procedure 展开的 process 也是递归的。区分递归和迭代的核心是是否需要辅助空间跟踪程序运行的状态。

Case analysis is more powerful than you thought! Trust me.

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