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)))))
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