SICP 問題1.9
(define (+ a b) (if (= a 0) b (inc (+ (dec a) b)))) ;; 再帰的 (+ 4 5) (inc (+ 3 5)) (inc (inc (+ 2 5))) (inc (inc (inc (+ 1 5)))) (inc (inc (inc (inc (+ 0 5))))) (inc (inc (inc (inc 5)))) (inc (inc (inc 6))) (inc (inc 7)) (inc 8) 9 (define (+ a b) (if (= a 0) b (+ (dec a) (inc b)))) ;; 反復的 (+ 4 5) (+ 3 6) (+ 2 7) (+ 1 8) 9