code: //==============================================================================
  //	
  //	Copyright (c) 2002-
  //	Authors:
  //	* Dave Parker <david.parker@comlab.ox.ac.uk> (University of Oxford)
  //	
  //------------------------------------------------------------------------------
  //	
  //	This file is part of PRISM.
  //	
  //	PRISM 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.
  //	
  //	PRISM 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 PRISM; if not, write to the Free Software Foundation,
  //	Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  //	
  //==============================================================================
  
  package simulator.sampler;
  
  import simulator.*;
  import prism.*;
  import parser.ast.*;
  
  public class SamplerRewardInstDisc extends SamplerDouble
  {
  	private int time;
  	private int rewardStructIndex;
  
  	/**
  	 * Construct a sampler for a (discrete-time) instantaneous reward property.
  	 * Passed in ExpressionTemporal should be a property of this type.
  	 * Reward structure index should also be specified.
  	 * All constants should have already been evaluated/replaced.
  	 */
  	public SamplerRewardInstDisc(ExpressionTemporal expr, int rewardStructIndex) throws PrismException
  	{
  		// Make sure expression is of the correct type
  		// Then extract other required info
  		if (expr.getOperator() != ExpressionTemporal.R_I)
  			throw new PrismException("Error creating Sampler");
  		time = expr.getUpperBound().evaluateInt();
  		this.rewardStructIndex = rewardStructIndex;
  		// Initialise sampler info
  		reset();
  		resetStats();
  	}
  
  	@Override
  	public boolean update(Path path, TransitionList transList) throws PrismLangException
  	{
  		// If the answer is already known we should do nothing
  		if (valueKnown)
  			return true;
  		
  		// As soon as time bound reached, store current state reward
  		if (path.size() == time) {
  			valueKnown = true;
  			value = path.getCurrentStateReward(rewardStructIndex);
  		}
  		// Or, if we are now at a deadlock
  		else if (transList != null && transList.isDeadlock()) {
  			valueKnown = true;
  			value = path.getCurrentStateReward(rewardStructIndex);
  		}
  		// Otherwise, don't know
  		
  		return valueKnown;
  	}
  	
  	@Override
  	public boolean needsBoundedNumSteps()
  	{
  		// Always bounded
  		return true;
  	}
  }
  