From: Ramakrishnan Muthukrishnan <vu3rdd@gmail.com>
Date: Wed, 25 Aug 2010 19:35:13 +0000 (+0530)
Subject: 2.2.4 in Scheme
X-Git-Url: https://git.rkrishnan.org/vdrive/%22news.html/simplejson/?a=commitdiff_plain;h=47c998cca118e8ef830ff8397eb7e77707903172;p=sicp.git

2.2.4 in Scheme
---

diff --git a/src/sicp/ch2_2.scm b/src/sicp/ch2_2.scm
new file mode 100644
index 0000000..8d03232
--- /dev/null
+++ b/src/sicp/ch2_2.scm
@@ -0,0 +1,44 @@
+#lang scheme
+
+(require (planet soegaard/sicp:2:1/sicp))
+
+(define (square-of-four tl tr bl br)
+  (lambda (painter)
+    (let ((top (beside (tl painter) (tr painter)))
+          (bottom (beside (bl painter) (br painter))))
+      (below bottom top))))
+
+(define (flipped-pairs painter)
+  (let ((combine4 (square-of-four identity flip-vert
+                                  identity flip-vert)))
+    (combine4 painter)))
+
+(define (identity x) x)
+
+(define (corner-split painter n)
+  (if (= n 0)
+      painter
+      (let ((up (up-split painter (- n 1)))
+            (right (right-split painter (- n 1))))
+        (let ((top-left (beside up up))
+              (bottom-right (below right right))
+              (corner (corner-split painter (- n 1))))
+          (beside (below painter top-left)
+                  (below bottom-right corner))))))
+
+(define (right-split painter n)
+  (if (= n 0)
+      painter
+      (let ((smaller (right-split painter (- n 1))))
+        (beside painter (below smaller smaller)))))
+
+(define (up-split painter n)
+  (if (= n 0)
+      painter
+      (let ((smaller (up-split painter (- n 1))))
+        (below painter (beside smaller smaller)))))
+
+(define (square-limit painter n)
+  (let ((combine4 (square-of-four flip-horiz identity
+                                  rotate180 flip-vert)))
+    (combine4 (corner-split painter n))))