#|
	$Id: term.lisp,v 1.4 2009/01/22 04:08:39 marek Exp $	
  *--------------------------------------------------------------------------*
  |  Copyright (C) 1994, Marek Rychlik (e-mail: rychlik@math.arizona.edu)    |
  |    Department of Mathematics, University of Arizona, Tucson, AZ 85721    |
  |                                                                          |
  | Everyone is permitted to copy, distribute and modify the code in this    |
  | directory, as long as this copyright note is preserved verbatim.         |
  *--------------------------------------------------------------------------*
|#

(defpackage "TERM"
  (:use "MONOM" "COEFFICIENT-RING" "COMMON-LISP")
  (:export term-divides-p  term*  term/ term-coefficient term-monom monom-times-term))

(in-package "TERM")

#+debug(proclaim '(optimize (speed 0) (debug 3)))
#-debug(proclaim '(optimize (speed 3) (debug 0)))

;;----------------------------------------------------------------
;; Basic operations on terms
;;----------------------------------------------------------------
;; THE REPRESENTATION: Terms are cons cells consisting
;; of a monom and coefficient
;;
;;	term:		(monom . coefficient)
;;
;;----------------------------------------------------------------
;; EXAMPLES: Suppose that variables are x and y. Then
;; Term  3*x*y^2 ---> ((1 2) . 3) 
;;----------------------------------------------------------------

;; Multiplication of terms
(defun term* (term1 term2 &optional (ring *coefficient-ring*))
  (cons 
   (monom* (car term1) (car term2))
   (funcall (ring-* ring) (cdr term1) (cdr term2))))

;;;; Division of terms
(defun term/ (term1 term2 &optional (ring *coefficient-ring*))
  (cons 
   (monom/ (car term1) (car term2))
   (funcall (ring-/ ring) (cdr term1) (cdr term2))))

;; Multiply monomial by term
(defun monom-times-term (m term)
  (cons (monom* m (car term)) (cdr term)))

;; Whether a term divides another term
(defun term-divides-p (term1 term2)
  (monom-divides-p (car term1) (car term2)))

;; Accessor functions
(defmacro term-monom (term) `(car ,term))
(defmacro term-coefficient (term) `(cdr ,term))

;; Setf methods
(defsetf term-monom (term) (monom)
  `(setf (car ,term) ,monom))

(defsetf term-coefficient (term) (coefficient)
  `(setf (cdr ,term) ,coefficient))