/*______________________________________________________________________________
 * 
 * Copyright 2005 Arnaud Bailly - NORSYS/LIFL
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * (1) Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 * (2) Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in
 *     the documentation and/or other materials provided with the
 *     distribution.
 *
 * (3) The name of the author may not be used to endorse or promote
 *     products derived from this software without specific prior
 *     written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 *  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Created on 10 mai 2005
 *
 */
package rationals.expr;

import rationals.algebra.SemiRing;

/**
 * A letter expression is simply a wrapper over any object. 
 * Note that the semantics of equals and hashcode must be properly
 * implemented by the wrapped object as this may be used in 
 * Collections, for example as keys in hashtables.
 * 
 * @author nono
 * @version $Id: Letter.java 2 2006-08-24 14:41:48Z oqube $
 */
public class Letter extends RationalExpr {

    private Object label;

    public static final Letter epsilon = new Letter(null) {

        public boolean equals(Object o) {
            return o == epsilon;
        }
        

        public SemiRing mult(SemiRing s2) {
            return s2;
        }
        
        public String toString() {
            return "1";
        }

        public int hashCode() {
            return 0;
        }
    };

    /**
     * Construct a new letter expression.
     * 
     * @param o
     *            label of the letter. May not be null. (use epsilon constant).
     */
    public Letter(Object o) {
        this.label = o;
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Object#equals(java.lang.Object)
     */
    public boolean equals(Object obj) {
        Letter lt = (Letter) obj;
        if (lt == null)
            return false;
        return lt.label == null ? this.label == null : lt.label.equals(label);
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Object#hashCode()
     */
    public int hashCode() {
        return label.hashCode();
    }

    /*
     * (non-Javadoc)
     * 
     * @see java.lang.Object#toString()
     */
    public String toString() {
        return label.toString();
    }
}