练习4-5 原文 Exercise 4.5. Scheme allows an additional syntax for cond clauses, ( => ). If evaluates to a true value, then is evaluated. Its value must be a procedure of one arg...

赋值 因为Scheme是函数式语言，通常来说，你可以编写不使用赋值的语句。然后如果使用赋值的话，有些算法就可以轻易实现了。尤其是内部状态和继续（continuations）需要赋值。 R5RS中规定的用...

练习4-3 原文 Exercise 4.3. Rewrite eval so that the dispatch is done in data-directed style. Compare this with the datadirected differentiation procedure of exercise 2.73. (You ...

练习4-4 原文 Exercise 4.4. Recall the definitions of the special forms and and or from chapter 1: ● and: The expressions are evaluated from left to right. If any expression eva...

练习4-2 原文 Exercise 4.2. Louis Reasoner plans to reorder the cond clauses in eval so that the clause for procedure applications appears before the clause for assignments. He a...

和上一节的引用类似，指针（pointer）是“指向（point to）”另外一种类型的复合类型。与引用类似，指针也实现了对其他对象的间接访问。然后指针和引用相比有许多不同。其一，指针本身就是一...

上一篇博文对应的是书中的第一章的一二两节，我们已经大致的有了一种构造的感觉不是么。书中展示了很多有趣的句法（syntax）。现在我们要让思想进一步的抽象，写这篇博客的时候并未学完整本书...