练习3-67

原文

Exercise 3.67. Modify the pairs procedure so that (pairs integers integers) will produce the stream of all pairs of integers (i,j) (without the condition i < j). Hint: You will need to mix in an additional stream.

代码

(define (all-pairs s t)
        (cons-stream 
                (list (stream-car s) (stream-car t))
                (interleave
                        (interleave
                                (stream-map (lambda (x) (list (stream-car s) x))
                                                        (stream-cdr t))
                                (all-pairs (stream-cdr s) (stream-cdr t)))
                        (stream-map (lambda (x) (list x (stream-car t)))
                                                (stream-cdr s)))))