Exercise 4.36 · 习题

Exercise 4.36: Exercise 3.69 discussed how

to generate the stream of all Pythagorean triples, with no upper bound

on the size of the integers to be searched. Explain why simply replacing

an-integer-between by an-integer-starting-from in the procedure

in Exercise 4.35 is not an adequate way to generate arbitrary Pythagorean

triples. Write a procedure that actually will accomplish this. (That is,

write a procedure for which repeatedly typing try-again would in

principle eventually generate all Pythagorean triples.)

练习 4.36：练习 3.69 讨论了如何生成所有勾股数组的流，其中对所搜索整数的大小没有上界。请解释为什么仅仅将练习 4.35 中过程里的 an-integer-between 换成 an-integer-starting-from，并不是生成任意勾股数组的合适方法。请编写一个实际能完成这一任务的过程。（即编写一个过程，对它反复输入 try-again，原则上最终能生成所有的勾股数组。）