solution to 2.91

diff --git a/src/sicp/ex2_91.rkt b/src/sicp/ex2_91.rkt
new file mode 100644 (file)
index 0000000..a0a7462
--- /dev/null
+++ b/src/sicp/ex2_91.rkt
@@ -0,0 +1,29 @@
+#lang racket
+
+(define (div-terms L1 L2)
+  (if (empty-termlist? L1)
+      (list (the-empty-termlist) (the-empty-termlist))
+      (let ((t1 (first-term L1))
+            (t2 (first-term L2)))
+        (if (> (order t2) (order t1))
+            (list (the-empty-termlist) L1)
+            (let ((new-c (div (coeff t1) (coeff t2)))
+                  (new-o (- (order t1) (order t2))))
+              (let ((rest-of-result
+                     (div-terms (sub-terms L1
+                                           (mul-term-by-all-terms (make-term new-o new-c)
+                                                                  L2))
+                                L2)))
+                (list (adjoin-term (make-term new-o new-c) 
+                                   (car rest-of-result))
+                      (cadr rest-of-result))))))))
+
+(define (div-poly P1 P2)
+  (if (same-variable? (variable P1)
+                      (variable P2))
+      (let ((t1 (term-list P1))
+            (t2 (term-list P2)))
+        (let ((div-results (div-terms t1 t2)))
+          (list (make-poly (variable P1) (car div-results))
+                (make-poly (variable P1) (cadr div-results)))))
+      (error "Polynomials are not of the same variable -- DIV-POLY")))
\ No newline at end of file