Add 2.2, 2.3 and 2.4

2_2.sch

@@ -0,0 +1,28 @@
+(define (make-point x y) (cons x y))
+
+(define (x-point p) (car p))
+(define (y-point p) (cdr p))
+
+(define (make-segment start end) (cons start end))
+(define (start-segment s) (car s))
+(define (end-segment s) (cdr s))
+
+(define (mid-point s)
+  (let ((start-x (x-point (start-segment s)))
+        (start-y (y-point (start-segment s)))
+        (end-x   (x-point (end-segment s)))
+        (end-y   (y-point (end-segment s))))
+    (make-point
+      (average start-x end-x)
+      (average start-y end-y))))
+
+(define (print-point p)
+  (display "(")
+  (display (x-point p))
+  (display ",")
+  (display (y-point p))
+  (display ")")
+  (newline))
+
+(define (average x y)
+  (/ (+ x y) 2.0))

2_3.sch

@@ -0,0 +1,40 @@
+(load "2_2.sch")
+
+(define (make-rect-corners top-left bottom-right)
+  (let ((top-right 
+	  (make-point (x-point bottom-right) (y-point top-left)))
+	(bottom-left
+	  (make-point (x-point top-left) (y-point bottom-right))))
+       (list top-left top-right bottom-right bottom-left)))
+
+(define (make-rect-size bottom-left width height)
+  (let ((top-left
+	  (make-point (x-point bottom-left) 
+		      (+ height (y-point bottom-left))))
+	(top-right
+	  (make-point (+ width (x-point bottom-left))
+		      (+ height (y-point bottom-left))))
+	(bottom-right
+	  (make-point (+ width (x-point bottom-left))
+		      (y-point bottom-left))))
+	(list top-left top-right bottom-right bottom-left)))
+
+
+(define (rect-top-left r) (car r))
+(define (rect-top-right r) (cadr r))
+(define (rect-bottom-right r) (caddr r))
+(define (rect-bottom-left r) (cadddr r))
+
+(define (perimeter r)
+  (let ((tl (rect-top-left r))
+	(br (rect-bottom-right r)))
+       (+
+       	(* 2 (abs (- (x-point br) (x-point tl))))
+       	(* 2 (abs (- (y-point br) (y-point tl)))))))
+
+(define (area r)
+  (let ((tl (rect-top-left r))
+	(br (rect-bottom-right r)))
+       (*
+	(abs (- (x-point tl) (x-point br)))
+	(abs (- (y-point tl) (y-point br))))))

2_4.sch

@@ -0,0 +1,8 @@
+(define (cons x y)
+  (lambda (m) (m x y)))
+
+(define (car z)
+  (z (lambda (p q) p)))
+
+(define (cdr z)
+  (z (lambda (p q) q)))