Add dense termlist representation

2_78.rkt

@@ -634,6 +634,60 @@
          (tag (negate-termlist termlist))))
   'done)
 
+(define (install-dense-package)
+
+  (define (highest-order-term term-list)
+    (- (length term-list) 1))
+
+  (define empty-termlist? null?)
+
+  (define (adjoin-term term term-list)
+    (define (zero-pad order term-list)
+      (if (= order (highest-order-term term-list))
+          term-list
+          (zero-pad order (cons 0 term-list))))
+    (let ((term-list-order (highest-order-term term-list)))
+      (cond ((and (null? term-list)
+                  (= (order term) 0))
+             (list (coeff term)))
+            ((= (order term) (+ term-list-order 1))
+             (cons (coeff term) term-list))
+            ((= (coeff term) 0)
+             term-list)
+            (else
+             (cons (coeff term)
+                   (zero-pad
+                    (- (order term) 1)
+                    term-list))))))
+
+  (define (tag l) (attach-tag 'dense l))
+
+  ;; Constructors
+  (put 'the-empty-termlist 'dense
+       (lambda () (tag '())))
+
+  (put 'adjoin-term '(term dense)
+       (lambda (term termlist)
+         (tag (adjoin-term
+               (apply make-term term)
+               termlist))))
+
+  ;; Selectors
+  (put 'first-term '(dense)
+       (lambda (termlist)
+         (make-term
+          (highest-order-term termlist)
+          (car termlist))))
+
+  (put 'rest-terms '(dense)
+       (lambda (termlist)
+         (tag (cdr termlist))))
+
+  (put 'empty-termlist? '(dense)
+       empty-termlist?)
+  
+  'done)
+
 (define (install-term-package)
   (define (make-term order coeff)
     (tag (list order coeff)))
@@ -748,6 +802,7 @@
 (install-complex-package)
 (install-termlist-package)
 (install-sparse-package)
+(install-dense-package)
 (install-term-package)
 (install-polynomial-package)
 
@@ -774,41 +829,6 @@
 ;; It isn't possible to coerce from one to the other, so a mixed-type operator is needed, and this
 ;; approach would fail.
 
-(define (highest-order-term term-list)
-  (length term-list))
-
-(define (make-term-dense order coeff) (list order coeff))
-(define (order-dense term) (car term))
-(define (coeff-dense term) (cadr term))
-(define first-term-dense car)
-(define (rest-terms-dense term-list)
-  (cdr term-list))
-(define (make-termlist-dense coeffs)
-  (cond ((null? coeffs) '())
-        ((= 0 (car coeffs))
-         (make-termlist-dense (cdr coeffs)))
-        (else (cons (car coeffs)
-                    (make-termlist-dense (cdr coeffs))))))
-(define the-empty-termlist-dense '())
-(define empty-termlist-dense? null?)
-
-(define (adjoin-term-dense term term-list)
-  (let ((term-list-order (highest-order-term term-list)))
-    (cond ((and (= (order term) 1)
-                (= term-list-order 0))
-           (make-termlist-dense (list (coeff term))))
-          ((= (order term) term-list-order)
-           (make-termlist-dense
-            (cons (add (coeff term)
-                       (first-term term-list))
-                  (rest-terms term-list))))
-          ((> (order term) term-list-order)
-           (make-termlist-dense
-            (cons (coeff term)
-                  (adjoin-term-dense
-                   (make-term-dense (- (order term) 1) 0)
-                   term-list))))
-          (else (adjoin-term-dense term (rest-terms term-list))))))