Exercise 1.5 · 习题

Exercise 1.5: Ben Bitdiddle has invented a test
to determine whether the interpreter he is faced with is using
applicative-order evaluation or normal-order evaluation. He defines the
following two procedures:

(define (p) (p))

(define (test x y)
(if (= x 0)
0
y))

Then he evaluates the expression

(test 0 (p))

What behavior will Ben observe with an interpreter that uses applicative-order

evaluation? What behavior will he observe with an interpreter that uses

normal-order evaluation? Explain your answer. (Assume that the evaluation

rule for the special form if is the same whether the interpreter is

using normal or applicative order: The predicate expression is evaluated first,

and the result determines whether to evaluate the consequent or the alternative

expression.)

练习 1.5：Ben Bitdiddle 发明了一种测试方法，用于判断他所面对的解释器使用的是应用序求值还是正则序求值。他定义了以下两个过程：

(define (p) (p))

(define (test x y)
(if (= x 0)
0
y))

然后他求值表达式

(test 0 (p))

使用应用序求值的解释器会表现出什么行为？使用正则序求值的解释器又会表现出什么行为？请解释你的回答。（假定特殊形式 if 的求值规则无论解释器使用正则序还是应用序都相同：先对谓词表达式求值，其结果决定是对推论表达式还是替代表达式求值。）