ubc.cs.JLog.Foundation.jGoal Maven / Gradle / Ivy
/*
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 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
*/
//#########################################################################
// jGoal
//#########################################################################
package ubc.cs.JLog.Foundation;
import java.lang.*;
import java.util.*;
import ubc.cs.JLog.Terms.*;
/**
* This abstract class specifies the behaviour for a goal.
* The jGoal class is designed to work in conjunction with
* iGoalStacks and with jProver.
* jGoals provide services for proving and retrying goals, and
* in the process they must correctly update the goal and
* proved stacks for jProver.
* Each jGoal is associated to some type of provable predicate,
* which provides some type of prove member function to perform
* the actual proof (or evaluation). The jGoal is responsible
* for updating the goal stacks as needed.
*
* @author Glendon Holst
* @version %I%, %G%
*/
abstract public class jGoal implements iNameArity
{
public jGoal()
{
};
/**
* Attempt to prove the goal represented by this jGoal.
* Goal must not be on either stack to prove (pop off goals stack before prove call).
* Goal must place itself on the appropriate stack before returning.
* proved stack if 'proved', goals stack otherwise.
* Since proved doesn't pop the stack we don't need a try/catch block.
* Must be called at least once before calling retry.
*
* @param goals iGoalStack containing goals yet to be proved.
* @param proved iGoalStack containing evaluated goals (goals
* that may already be proved, or awaiting their child goals
* to be proved).
*
* @return boolean is true if this goal ended up on
* proved, false otherwise.
*/
abstract public boolean prove(iGoalStack goals,iGoalStack proved);
/**
* Attempt to prove the goal represented by this jGoal.
* Goal must not be on either stack to retry (pop off proved stack before retry call).
* Goal must place itself on the goal stack, and normally need not pop either stack.
* Since retry doesn't pop the stack we don't need a try/catch block.
*
* @param goals iGoalStack containing goals yet to be proved.
* @param proved iGoalStack containing evaluated goals (goals
* that may already be proved, or awaiting their child goals
* to be proved).
*
* @return boolean is true if the prover should attempt
* a prove on this goal, false otherwise.
*/
abstract public boolean retry(iGoalStack goals,iGoalStack proved);
/**
* Make a rule on the proved stack clean up children on the goal stack.
* Should be called from within retry, and should rely on
* retry to adjust the proved stack. this remains on proved stack.
*
* @param goals iGoalStack containing goals yet to be proved.
*/
protected void internal_remove(iGoalStack goals) {};
/**
* Combines internal_remove with a full restart and resoration of
* any previous variable state. May be called by other goals, such as a
* jCutGoal. this is still located on proved stack.
*
* @param goals iGoalStack containing goals yet to be proved.
*/
public void internal_restore(iGoalStack goals) {};
public jGoal next = null; // only iGoalStack should access this member
};