ubc.cs.JLog.Terms.jBuiltinPredicate Maven / Gradle / Ivy

Go to download
/*
    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 
*/
//#########################################################################
//	BuiltinPredicate
//#########################################################################
 
package ubc.cs.JLog.Terms;

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

/**
 * This is the abstract base for builtin predicates. The parser must create the 
 * appropriate object for builtin predicates. Builtins do not appear in the database
 * and are designed to provide a way to optimize a predicate or provide additional 
 * functionallity.
 *  
 * @author       Glendon Holst
 * @version      %I%, %G%
 */
abstract public class jBuiltinPredicate extends iPredicate
{
 public jBuiltinPredicate()
 {
  type = TYPE_BUILTINPREDICATE;
 };

 public int 		getArity()
 {
  return 0;
 };

 /**
  * Compares predicate aguments. Override in classes with different arities.
  */
 protected int 		compareArguments(iPredicate ipred,boolean first_call,boolean var_equal)
 {
  if (ipred instanceof jBuiltinPredicate && getArity() == 0)
  {jBuiltinPredicate 		bip = (jBuiltinPredicate) ipred;
   int 			compare_val;
   int 			arity_b;
   
   arity_b = bip.getArity();
   
   if (0 < arity_b)
    return LESS_THAN;
   else if (0 > arity_b)
    return GREATER_THAN;
   
   compare_val = getName().compareTo(bip.getName());
   
   if (compare_val < 0)
    return LESS_THAN;
   if (compare_val > 0)
    return GREATER_THAN;
   return EQUAL;
  }
  
  return (first_call ? -ipred.compareArguments(this,false,var_equal) : EQUAL);
 };

 public boolean 	isConsultNeeded()
 {
  return false; // builtins without arguments don't need consulting
 };

 public boolean 	equivalence(jTerm term,jEquivalenceMapping v)
 {jTerm t = term.getTerm();
 
  // only unify with other predicate terms
  if (type != t.type)
   return false;

  // altough we cannot be certain that term is a jBuiltinPredicate, if it is not then 
  // type was wrong so this warrents a failing exception.
  {jBuiltinPredicate 		pterm;
   
   pterm = (jBuiltinPredicate) t;
   
   // predicates must have same name
   if (!getName().equals(pterm.getName()))
    return false;
 
  // only test if terms have same arity
   if (getArity() != pterm.getArity())
    return false;

   // arguments must be equivalent.  subclasses defining new arguments should handle.
   return equivalenceArguments(pterm,v);
  }
 };

 /**
  * Unification. For builtin predicates, unification may happen when they 
  * are arguments to predicates.
  */
 public boolean 	unify(jTerm term,jUnifiedVector v)
 {
  // if term is variable we let it handle the unification
  if (term.type == TYPE_VARIABLE)
   return term.unify(this,v);
   
  // only unify with other predicate terms
  if (type != term.type)
   return false;

  // altough we cannot be certain that term is a jBuiltinPredicate, if it is not then 
  // type was wrong so this warrents a failing exception.
  {jBuiltinPredicate 		pterm;
   
   pterm = (jBuiltinPredicate) term;
   
   // predicates must have same name
   if (!getName().equals(pterm.getName()))
    return false;
 
  // only unify if terms have same arity
   if (getArity() != pterm.getArity())
    return false;

   // arguments must unify.  subclasses defining new arguments should handle.
   return unifyArguments(pterm,v);
  }
 };
 
 /**
  * Equivalence test arguments. Similar behavior to that of equivalence.
  *
  * @param pterm 	We are assured that pterm has the same type, name, and arity.  
  * @param v 		same as jEquivalenceMapping parameter in 
  * 			equivalence.  
  *
  * @return 		Should test for instanceof as required and return false if there
  * 			is no match, true otherwise.
  */
 protected boolean 	equivalenceArguments(jBuiltinPredicate pterm,jEquivalenceMapping v)
 {
  return true;
 };

 /**
  * Unification of arguments. Similar behavior to that of unify.
  *
  * @param pterm 	We are assured that pterm has the same type, name, and arity.  
  * @param v 		same as jUnifiedVector parameter in 
  * 			unify.  
  *
  * @return 		Should test for instanceof as required and return false if there
  * 			is no match, true otherwise.
  */
 protected boolean 	unifyArguments(jBuiltinPredicate pterm,jUnifiedVector v)
 {
  return true;
 };
 
 public void 		registerVariables(jVariableVector v)
 {
 };

 public void 		enumerateVariables(jVariableVector v,boolean all)
 {
 };
 
 public jTerm 		duplicate(jVariable[] vars)
 {
  return this;  // in many cases builtins are constant, so don't duplicate
 };

 public jTerm 		copy(jVariableRegistry vars)
 {
  return this;  // in many cases builtins are constant, so don't duplicate
 };

 public String 		toString(boolean usename)
 {
  return getName();
 };
};