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