DifferenceExt.java

/*
 * DifferenceExt.java
 *
 * Copyright (C) 2008  Pei Wang
 *
 * This file is part of Open-NARS.
 *
 * Open-NARS 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.
 *
 * Open-NARS 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with Open-NARS.  If not, see <http://www.gnu.org/licenses/>.
 */
package nars.language;

import java.util.TreeSet;
import nars.io.Symbols.NativeOperator;
import static nars.language.DifferenceInt.ensureValidDifferenceArguments;

/**
 * A compound term whose extension is the difference of the extensions of its term
 */
public class DifferenceExt extends CompoundTerm {

    /**
     * Constructor with partial values, called by make
     * @param n The name of the term
     * @param arg The component list of the term
     */
    private DifferenceExt(Term[] arg) {
        super(arg);
        
        ensureValidDifferenceArguments(arg);        
        
        init(arg);
    }


    /**
     * Clone an object
     * @return A new object, to be casted into a DifferenceExt
     */
    @Override
    public DifferenceExt clone() {
        return new DifferenceExt(term);
    }

    @Override public Term clone(Term[] replaced) {
        return make(replaced);
    }

    
    /**
     * Try to make a new DifferenceExt. Called by StringParser.
     * @return the Term generated from the arguments
     * @param arg The list of term
     * @param memory Reference to the memory
     */
    public static Term make(Term[] arg) {
        if (arg.length == 1) { // special case from CompoundTerm.reduceComponent
            return arg[0];
        }
        if (arg.length  != 2) {
            return null;
        }
        if ((arg[0] instanceof SetExt) && (arg[1] instanceof SetExt)) {
            //TODO maybe a faster way to do this operation:
            TreeSet<Term> set = new TreeSet<>(((CompoundTerm) arg[0]).asTermList());
            set.removeAll(((CompoundTerm) arg[1]).asTermList());           // set difference
            return SetExt.make(set);
        }                
        
        if (arg[0].equals(arg[1])) {
            return null;
        }
        
        return new DifferenceExt(arg);
    }

    /**
     * Try to make a new compound from two term. Called by the inference rules.
     * @param t1 The first component
     * @param t2 The second component
     * @param memory Reference to the memory
     * @return A compound generated or a term it reduced to
     */
    public static Term make(final Term t1, final Term t2) {
        if (t1.equals(t2))
            return null;

        return make(new Term[]{t1,t2});
    }

    /**
     * Get the operator of the term.
     * @return the operator of the term
     */
    @Override
    public NativeOperator operator() {
        return NativeOperator.DIFFERENCE_EXT;
    }
}