手続きによる抽象の構築(11)

(define (+ a b)
(if (= a 0)
b
(inc (+ (dec a) b))))
(+ 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))))
(+ 4 5)
(+ (dec 4) (inc 5))
(+ (dec 3) (inc 6))
(+ (dec 2) (inc 7))
(+ (dec 1) (inc 8))
9