SICP in Clojure: Chapter 1, Exercise 9

This is my Clojure solution to Chapter 1, Exercise 9:

(ns sicp.ch1.ex09)

(defn add-1
  [a b]
  (if (zero? a)
    b
    (inc (add-1 (dec a) b))))

(defn add-2
  [a b]
  (if (zero? a)
    b
    (add-2 (dec a) (inc b))))

(add-1 5 10) ; => 15 -- a recursive process


(add-2 5 10) ; => 15 -- an iterative process