From 9387d46dc07f0da16fb263fe1b1e0768617d8b5e Mon Sep 17 00:00:00 2001
From: Denis Smet <denis.smetannikov@yandex.ru>
Date: Sun, 15 Oct 2023 21:37:43 +0400
Subject: [PATCH] Exercise 1.9

---
 src/sicp/chapter_1/ex_1_9.clj       | 20 ++++++++++++++++++++
 test/sicp/chapter_1/ex_1_9_test.clj | 11 +++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 src/sicp/chapter_1/ex_1_9.clj
 create mode 100644 test/sicp/chapter_1/ex_1_9_test.clj

diff --git a/src/sicp/chapter_1/ex_1_9.clj b/src/sicp/chapter_1/ex_1_9.clj
new file mode 100644
index 0000000..ce055b2
--- /dev/null
+++ b/src/sicp/chapter_1/ex_1_9.clj
@@ -0,0 +1,20 @@
+(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?
diff --git a/test/sicp/chapter_1/ex_1_9_test.clj b/test/sicp/chapter_1/ex_1_9_test.clj
new file mode 100644
index 0000000..17ebaf2
--- /dev/null
+++ b/test/sicp/chapter_1/ex_1_9_test.clj
@@ -0,0 +1,11 @@
+(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)))
+  )