source: branches/f4grobner/integer-ring.lisp@ 4303

;;; -*-  Mode: Lisp -*- 
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;;;                                                                              
;;;  Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>          
;;;                                                                              
;;;  This program is free software; you can redistribute it and/or modify        
;;;  it under the terms of the GNU General Public License as published by        
;;;  the Free Software Foundation; either version 2 of the License, or           
;;;  (at your option) any later version.                                         
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;;;  This program is distributed in the hope that it will be useful,             
;;;  but WITHOUT ANY WARRANTY; without even the implied warranty of              
;;;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the               
;;;  GNU General Public License for more details.                                
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;;;  You should have received a copy of the GNU General Public License           
;;;  along with this program; if not, write to the Free Software                 
;;;  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  
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(defpackage "INTEGER-RING"
  (:use :cl :copy :ring :rational-field)
  (:export "INTEGER-RING"
           "INTEGER-RING-VALUE"
           "ADD-TO"
           "SUBTRACT-FROM"
           "MULTIPLY-BY"
           "DIVIDE-BY"
           "UNARY-MINUS"
           "UNARY-INVERSE"
           "UNIVERSAL-GCD"
           "UNIVERSAL-EZGCD"
           "UNIVERSAL-EQUALP"
           "UNIVERSAL-ZEROP"
           "->SEXP")
  (:documentation "Wraps integers into an object."))

(in-package "INTEGER-RING")

(defclass integer-ring (rational-field)
  ((value :initarg :value :initform 0 :accessor integer-ring-value :type integer))
  (:documentation "An object representing an integer.")
  )
           
(defmethod print-object ((self integer-ring) stream)
  (print-unreadable-object (self stream :type t :identity t)
    (with-accessors ((value integer-ring-value))
        self
      (format stream "VALUE=~A" value))))

(defmethod unary-inverse ((self integer-ring))
  (with-slots (value)
      self
    (case value
      (1 self)
      (-1 self)
      (otherwise (error "Non-invertible ring element: ~S" self)))))

(defmethod universal-gcd ((self integer-ring) (other integer-ring))
  (with-slots (value)
      self
    (with-slots ((other-value value))
        other
      (make-instance 'integer-ring :value (gcd value other-value)))))

(defmethod universal-ezgcd ((object integer-ring) (other integer-ring))
  (with-slots (value)
      object
    (with-slots ((other-value value))
        other
      (let ((c (gcd value other-value)))
        (values (make-instance 'integer-ring :value c)
                (make-instance 'integer-ring :value (/ value c))
                (make-instance 'integer-ring :value (/ other-value c)))))))