1.2.4 completed

ex1.16.scm

@@ -0,0 +1 @@
+`xzc`xc

ex1.17.scm

@@ -0,0 +1,18 @@
+(define (even? n)
+  (= (remainder n 2) 0))
+
+(define (halve n)
+  (/ n 2))
+
+(define (double n)
+  (+ n n))
+
+(define (* a b)
+  (cond ((= b 0) 0)
+	((even? b) (* (double a) (halve b)))
+	(else (+ a (* a (- b 1))))))
+
+(* 2 2)
+(* 3 4)
+(* 15 11)
+

ex1.19.scm

@@ -0,0 +1,14 @@
+(define (fib n)
+  (fib-iter 1 0 0 1 n))
+
+(define (fib-iter a b p q count)
+  (cond ((= count 0) b)
+        ((even? count) (fib-iter a 
+				 b
+				 <??> ; compute p’
+				 <??> ; compute q’ (/ count 2)))
+        (else (fib-iter (+ (* b q) (* a q) (* a p))
+                        (+ (* b p) (* a q))
+                        p
+                        q
+                        (- count 1)))))