Exercise 3.69

Read Exercise 3.69 ~ Solution

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

(define pythagorean-triples
  (stream-filter (lambda (t)
                   (= (+ (square (car t))
                         (square (cadr t)))
                      (square (caddr t))))
                 (triples integers integers integers) ))

(show-stream pythagorean-triples 5)
(3 4 5)
(6 8 10)
(5 12 13)
(9 12 15)
(8 15 17)
done