From 91d3bafd2c5f864bb27556efd9dc4dd1885cb460 Mon Sep 17 00:00:00 2001
From: Oliver Payne <ompayne@gmail.com>
Date: Fri, 22 Apr 2022 14:44:15 +0100
Subject: [PATCH] Add exercise 3.8

---
 3_8.rkt | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 3_8.rkt

diff --git a/3_8.rkt b/3_8.rkt
new file mode 100644
index 0000000..541c9bb
--- /dev/null
+++ b/3_8.rkt
@@ -0,0 +1,24 @@
+#lang sicp
+
+(define f
+  (let ((x 0))
+    (lambda (n)
+      (let ((old-x x))
+        (begin
+          (set! x n)
+          (cond ((= n 0)
+                 (if (= old-x 0) -1 0))
+                (else n)))))))
+
+(define left-to-right
+  (let ((left (f 0))
+        (right (f 1)))
+    (+ left right)))
+
+(define right-to-left
+  (let ((right (f 1))
+        (left (f 0)))
+    (+ left right)))
+
+;; (f 0) first: (+ (f 0) (f 1)) -> 0
+;; (f 1) first: (+ (f 0) (f 1)) -> 1