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(defpackage :commodities
(:use :cl)
(:export :new-commodity
:name
:price
:commodity-eq))
(in-package :commodities)
(defclass commodity ()
((name :initarg :name
:reader name)
(price :initarg :price
:accessor price)))
(defun new-commodity (name price)
(when (> price 0)
(make-instance 'commodity
:name name
:price price)))
(defmethod print-object ((object commodity) stream)
(print-unreadable-object (object stream :type t)
(with-slots (name price) object
(format stream "~a worth ~a" name price))))
(defmethod commodity-eq ((c1 commodity) (c2 commodity))
(and (equal (name c1) (name c2))
(= (price c1) (price c2))))
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