//tabstop=4
//*****************************************************************************/
// Project: jpl
//
// File:    $Id: JVoid.java,v 1.2 2004/09/21 14:30:27 jan Exp $
// Date:    $Date: 2004/09/21 14:30:27 $
// Author:  Fred Dushin <fadushin@syr.edu>
//          
//
// Description:
//    
//
// -------------------------------------------------------------------------
// Copyright (c) 2004 Paul Singleton
// Copyright (c) 1998 Fred Dushin
//                    All rights reserved.
// 
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Library Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
// 
// This library 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 Library Public License for more details.
//*****************************************************************************/
package jpl;

import java.util.Map;

import jpl.fli.Prolog;
import jpl.fli.term_t;

//----------------------------------------------------------------------/
// JVoid
/**
 * A jpl.JVoid is a specialised Term.  Instances of this class
 * denote JPL 'jvoid' values in Prolog, i.e. @(void):
 * <pre>
 * JVoid b = new JVoid();
 * </pre>
 * A JVoid can be used (and re-used) in Compound Terms.
 * 
 * <hr><i>
 * Copyright (C) 2004  Paul Singleton<p>
 * Copyright (C) 1998  Fred Dushin<p>
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.<p>
 * 
 * This library 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 Library Public License for more details.<p>
 * </i><hr>
 * @author  Fred Dushin <fadushin@syr.edu>
 * @version $Revision: 1.2 $
 * @see jpl.Term
 * @see jpl.Compound
 */
public class JVoid extends Term {
	
	//==================================================================/
	//  Attributes (none)
	//==================================================================/

	//==================================================================/
	//  Constructors
	//==================================================================/

	/**
	 * This constructor creates a JVoid.
	 * 
	 */
	public JVoid() {
	}

	//==================================================================/
	//  Methods (common)
	//==================================================================/

	/**
	 * Returns a Prolog source text representation of this JVoid
	 * 
	 * @return  a Prolog source text representation of this JVoid
	 */
	public String toString() {
		return "@(void)";
	}

	/**
	 * Two JVoids are equal
	 * 
	 * @param   obj  The Object to compare (not necessarily another JVoid)
	 * @return  true if the Object satisfies the above condition
	 */
	public final boolean equals(Object obj) {
		return this == obj || (obj instanceof JVoid);
	}
	
	public final int type() {
		return Prolog.JVOID;
	}
	
	public String typeName(){
		return "JVoid";
	}
	
	//==================================================================/
	//  Methods (deprecated)
	//==================================================================/

	/**
	 * The (nonexistent) args of this JVoid
	 * 
	 * @return the (nonexistent) args of this JVoid
	 * @deprecated
	 */
	public Term[] args() {
		return new Term[] {};
	}
	
	/**
	 * Returns a debug-friendly representation of this JVoid
	 * 
	 * @return  a debug-friendly representation of this JVoid
	 * @deprecated
	 */
	public String debugString() {
		return "(JVoid)";
	}

	//==================================================================/
	//  Converting JPL Terms to Prolog terms
	//==================================================================/

	/**
	 * To convert a JVoid to a term, we unify the (freshly created, hence unbound)
	 * term_t with @(void).
	 * 
	 * @param   varnames_to_vars  A Map from variable names to Prolog variables.
	 * @param   term              A (previously created and unbound) term_t which is to be
	 *                            assigned a Prolog @(void) structure
	 */
	protected final void put(Map varnames_to_vars, term_t term) {
		Prolog.put_jvoid(term);
	}

	//==================================================================/
	//  Converting Prolog terms to JPL Terms
	//==================================================================/
	
	/**
	 * Converts a term_t to a JVoid.  Assuming the Prolog term to be
	 * @(void), we just create a new JVoid instance.
	 * NB This conversion is only invoked if "JPL-aware" term import is specified.
	 *
	 * @param   vars_to_Vars  A Map from Prolog variables to JPL Variables.
	 * @param   term          The term_t to convert
	 * @return                A new JVoid instance
	 */
	protected static Term getTerm(Map vars_to_Vars, term_t term) {
		return new jpl.JVoid();
	}

	//==================================================================/
	//  Computing Substitutions
	//==================================================================/

	/**
	 * Nothing needs to be done if the Term denotes an Atom, Integer, Float, JRef, JBoolean or JVoid
	 * 
	 * @param   varnames_to_Terms  A Map from variable names to Terms.
	 * @param   vars_to_Vars       A Map from Prolog variables to JPL Variables.
	 *                 Variables.
	 */
	protected final void getSubst(Map varnames_to_Terms, Map vars_to_Vars) {
	}

}

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