From: Ramakrishnan Muthukrishnan Date: Mon, 7 Jun 2010 17:29:43 +0000 (+0530) Subject: Solution to 2.3 X-Git-Url: https://git.rkrishnan.org/components/%22news.html//%22%22.?a=commitdiff_plain;h=50056e4d2bead21e6cfb6087fa21998fe70922a7;p=sicp.git Solution to 2.3 --- diff --git a/src/sicp/ex2_3.clj b/src/sicp/ex2_3.clj new file mode 100644 index 0000000..9185f63 --- /dev/null +++ b/src/sicp/ex2_3.clj @@ -0,0 +1,69 @@ +(ns sicp.ex2_3 + (:use [sicp ex2_2 utils] + [clojure.test])) + +(declare width-rect height-rect) +;; wishful thinking. Assume that constructors and selectors are +;; available. Now compute perimeter. +(defn perimeter-rect [rect] + (* 2 (+ (width-rect rect) + (height-rect rect)))) + +(defn area-rect [rect] + (* (width-rect rect) + (height-rect rect))) + +;; now implement the rectangle. One way to represent a rectangle +;; is to use a pair of points representing diagonal corners. +(defn make-rect [p1 p2] + (list p1 p2)) + +(defn p1-rect [r] + (first r)) + +(defn p2-rect [r] + (first (rest r))) + +(defn width-rect [r] + (let [p1 (p1-rect r) + p2 (p2-rect r)] + (abs (- (x-point p1) (x-point p2))))) + +(defn height-rect [r] + (let [p1 (p1-rect r) + p2 (p2-rect r)] + (abs (- (y-point p1) (y-point p2))))) + +(deftest test-rect-perimeter-square + (is (= (perimeter-rect (make-rect (make-point 0 0) (make-point 1 1))) 4))) + +(deftest test-rect-area-square + (is (= (area-rect (make-rect (make-point 0 0) (make-point 2 2))) 4))) + +;; part2 - another implementation +;; instead of coordinates, we store height and width itself. +(defn make-rect-1 [h w] + (list h w)) + +(defn width-rect-1 [r] + (first r)) + +(defn height-rect-1 [r] + (first (rest r))) + +;; the below routines are unmodified versions of the above +;; procedures, but renamed to work around the compiler. Is +;; there a simpler way? +(defn perimeter-rect-1 [rect] + (* 2 (+ (width-rect-1 rect) + (height-rect-1 rect)))) + +(defn area-rect-1 [rect] + (* (width-rect-1 rect) + (height-rect-1 rect))) + +(deftest test-rect-perimeter-square-1 + (is (= (perimeter-rect-1 (make-rect-1 1 1)) 4))) + +(deftest test-rect-area-square-1 + (is (= (area-rect-1 (make-rect-1 2 2)) 4)))