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/*
    This file is part of JLog.

    Created by Glendon Holst for Alan Mackworth and the 
    "Computational Intelligence: A Logical Approach" text.
    
    Copyright 1998, 2000, 2002 by University of British Columbia and 
    Alan Mackworth.
    
    This notice must remain in all files which belong to, or are derived 
    from JLog.
    
    Check  or 
     for further information
    about JLog, or to contact the authors.
     
    JLog 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.

    JLog 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 JLog; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    URLs:  or 
*/
//#########################################################################
//	Predicate
//#########################################################################
 
package ubc.cs.JLog.Terms;

import java.lang.*;
import java.util.*;
import ubc.cs.JLog.Foundation.*;

/**
* This is the abstract base class for Prolog predicates.
*  
* @author       Glendon Holst
* @version      %I%, %G%
*/
abstract public class iPredicate extends jTerm implements iNameArity
{
 protected int 		compare(jTerm term,boolean first_call,boolean var_equal)
 {jTerm 		t = term.getTerm();
 
  if ((t instanceof jVariable) || (t instanceof jReal) || (t instanceof jInteger))
   return GREATER_THAN;
  
  if (t instanceof iPredicate)
  {iPredicate 	ip = (iPredicate) t;
   int 			compare_val;
   int 			arity_a,arity_b;
   
   arity_a = getArity();
   arity_b = ip.getArity();
   
   if (arity_a < arity_b)
    return LESS_THAN;
   else if (arity_a > arity_b)
    return GREATER_THAN;
   
   compare_val = getName().compareTo(ip.getName());
   
   if (compare_val < 0)
    return LESS_THAN;
   if (compare_val > 0)
    return GREATER_THAN;

   return compareArguments(ip,true,var_equal);
  }
  
  return (first_call ? -t.compare(this,false,var_equal) : EQUAL);
 };

 /**
  * Compares the arguments for predicates. Like compare except that name 
  * and arity must be equal.
  *
  * @param ipred	the iPredicate to compare with this instance of 
  *			iPredicate.
  * @param first_call	true if just invoked by public 
  * 			compare member function.
  * 			false otherwise.
  * @param var_equal	if var_equal is true, then unbound 
  *			variables are considered equal.
  *                     var_equal = false is standard prolog 
  * 			behavior.
  * @return 		LESS_THAN if this instance is less than 
  * 			term, 
  * 			EQUAL if the two terms are equal, and 
  * 			GREATER_THAN if 
  * 			this instance is greater than term.
  */
 abstract protected int 	compareArguments(iPredicate ipred,
                                    boolean first_call,boolean var_equal);

 /**
  * Accessor for the arguments for this predicate. Don't modify arguments after consult. 
  * Arguments are not guaranteed to be original so modifying has an unspecified effect.
  *
  * @return 		The original or possibly duplicated arguments for this predicate.
  */
 public jCompoundTerm 		getArguments()
 {
  return new jCompoundTerm();
 };

 /**
  * Adds goal to prove this predicate onto goal stack. This version is called when 
  * the original predicate must duplicate itself (or its arguments).
  * Add goals in the reverse order you want them evaluated.
  *
  * @param g 		The super-goal jGoal for the sub-goal that this
  * 			function will add.
  * @param vars 	The vector of duplicate variables produced
  * 			from the previous call to registerVariables.  
  * 			Needed for call to duplicate.
  * @param goals 	The iGoalStack to add the goal to.
  */
 abstract public void 		addGoals(jGoal g,jVariable[] vars,iGoalStack goals); 
 
 /**
  * Adds goal to prove this predicate onto goal stack. This version is called when 
  * the original predicate is already duplicated (usually as part of an argument for 
  * another predicate). Add goals in the reverse order you want them evaluated.
  *
  * @param g 		The super-goal jGoal for the sub-goal that this
  * 			function will add.
  * @param goals 	The iGoalStack to add the goal to.
  */
 abstract public void 		addGoals(jGoal g,iGoalStack goals); 
};