【SICP练习】136 练习3.67

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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