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 parser.type;
  
  import param.BigRational;
  import prism.PrismLangException;
  
  public class TypeDouble extends Type 
  {
  	private static TypeDouble singleton;
  	
  	static
  	{
  		singleton = new TypeDouble();
  	}
  	
  	private TypeDouble()
  	{		
  	}	
  	
  	public boolean equals(Object o)
  	{
  		return (o instanceof TypeDouble);
  	}
  	
  	@Override
  	public String getTypeString()
  	{
  		return "double";
  	}
  	
  	@Override
  	public Object defaultValue()
  	{
  		return new Double(0.0);
  	}
  	
  	public static TypeDouble getInstance()
  	{
  		return singleton;
  	}
  	
  	@Override
  	public boolean canAssign(Type type)
  	{
  		return (type instanceof TypeDouble || type instanceof TypeInt);
  	}
  	
  	@Override
  	public Number castValueTo(Object value) throws PrismLangException
  	{
  		if (value instanceof Double)
  			return (Double) value;
  		if (value instanceof BigRational)
  			return (BigRational) value;
  		if (value instanceof Integer)
  			return new Double(((Integer) value).intValue());
  		else
  			throw new PrismLangException("Can't convert " + value.getClass() + " to type " + getTypeString());
  	}
  
  	@Override
  	public Object castFromBigRational(BigRational value) throws PrismLangException
  	{
  		return value.doubleValue();
  	}
  
  }
  