SICP問題3.54
mul-streamsの定義
(define (mul-streams s1 s2) (stream-map * s1 s2))
0から数えてn番目の要素がn+1の階乗となる定義
(define factorials (cons-stream 1 (mul-streams factorials (add-streams ones integers))))
テスト
(stream-ref factorials 0) ; 1 (stream-ref factorials 1) ; 2 (stream-ref factorials 2) ; 6 (stream-ref factorials 3) ; 24 (stream-ref factorials 4) ; 120 (stream-ref factorials 5) ; 720
OK