[12.24] [sicp 3.70]

[ruandao]

(load "stream.scm")
(load "stream-integers.scm")

(define (merge-weighted weight s t)
  (cond
   ((stream-null? s) t)
   ((stream-null? t) s)
   (else (let ((s1 (stream-car s))
           (t1 (stream-car t)))
       (cond
        ((< (weight s1) (weight t1))
         (cons-stream s1
              (merge-weighted weight
                      (stream-cdr s)
                      t)))
        ((> (weight s1) (weight t1))
         (cons-stream t1
              (merge-weighted weight
                      s
                      (stream-cdr t))))
        (else (cons-stream s1
                   (cons-stream t1
                        (merge-weighted
                         weight
                         (stream-cdr s)
                         (stream-cdr t))))))))))

(define (weighted-pairs weight s t)
  (cons-stream
   (list (stream-car s) (stream-car t))
   (merge-weighted weight
           (stream-map (lambda(x) (list (stream-car s) x))
                   (stream-cdr t))
           (weighted-pairs weight
                   (stream-cdr s)
                   (stream-cdr t)))))

#|

((lambda()
   (define (weight-by-sum p)
     (+ (car p) (cadr p)))
   (display (stream-head 'weighted-pair1
             (weighted-pairs weight-by-sum 
                     integers
                     integers) 10))
   (newline)
   (define (weight-by-poly p)
     (let ((i (car p))
       (j (cadr p)))
       (+ (* 2 i) (* 3 j) (* 5 i j))))
   (define (filter-2-3-5 x)
     (not (or (= (remainder x 2) 0)
          (= (remainder x 3) 0)
          (= (remainder x 5) 0))))
   (define filtered-integers
     ((lambda() (stream-filter filter-2-3-5 integers))))
   (display (stream-head 'weight-by-poly
             (weighted-pairs weight-by-poly
                     filtered-integers
                     filtered-integers)
             10))
   (newline)
))

|#