Exercise 4.25 · 习题

Exercise 4.25: Suppose that (in ordinary
applicative-order Scheme) we define unless as shown above and then
define factorial in terms of unless as

(define (factorial n)
(unless (= n 1)
(* n (factorial (- n 1)))
1))

What happens if we attempt to evaluate (factorial 5)? Will our

definitions work in a normal-order language?

练习 4.25：假设（在普通的应用序 Scheme 中）我们按上文定义了 unless，然后用 unless 来定义阶乘：

(define (factorial n)
(unless (= n 1)
(* n (factorial (- n 1)))
1))

如果我们尝试对 (factorial 5) 求值，会发生什么？这些定义在正则序语言中能正常工作吗？