Exercise 1.9

src/sicp/chapter_1/ex_1_9.clj

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+(ns sicp.chapter-1.ex-1-9)
+
+; Exercise 1.9
+; Each of the following two procedures defines a method for adding two positive integers
+; in terms of the procedures inc, which increments its argument by 1, and dec, which decrements its argument by 1.
+
+(defn plus
+  [a b]
+  (if (= a 0)
+    b
+    (inc (+ (dec a) b)))) ; linear recursive
+
+(defn plus-v2
+  [a b]
+  (if (= a 0)
+    b
+    (+ (dec a) (inc b)))) ; linear iteration
+
+; Using the substitution model, illustrate the process generated by each procedure in evaluating (+ 4 5).
+; Are these processes iterative or recursive?

test/sicp/chapter_1/ex_1_9_test.clj

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+(ns sicp.chapter-1.ex-1-9-test
+  (:require [clojure.test :refer :all]
+            [sicp.chapter-1.ex-1-9 :refer [plus plus-v2]]))
+
+(deftest plus-test
+  (is (= 3 (plus 1 2)))
+  )
+
+(deftest plus-v2-test
+  (is (= 3 (plus-v2 1 2)))
+  )