(wat-aro)

生きてます

SICP 問題 3.55

s0, s0 + s1, s0 + s1 + s2, ...
という要素なのでstreamの次の要素とsum-integersの今の要素を足したものがsum-integersの次の要素となる.

(define (partial-sums stream)
  (cons-stream (stream-car stream)
               (add-streams (stream-cdr stream)
                            sum-integers)))

(define sum-integers
  (partial-sums integers))
gosh> (stream-ref sum-integers 0)
1
gosh> (stream-ref sum-integers 1)
3
gosh> (stream-ref sum-integers 2)
6
gosh> (stream-ref sum-integers 3)
10
gosh> (stream-ref sum-integers 4)
15