Exercise 5.23 · 习题

Exercise 5.23: Extend the evaluator to handle

derived expressions such as cond, let, and so on

(4.1.2). You may “cheat” and assume that the syntax transformers such

as cond->if are available as machine operations.

练习 5.23：扩展求值器，使其能处理派生表达式，例如 cond、let 等（4.1.2 节）。你可以“取巧”，假设诸如 cond->if 之类的语法变换器可作为机器操作使用。