code: //==============================================================================
  //	
  //	Copyright (c) 2002-
  //	Authors:
  //	* Dave Parker <david.parker@comlab.ox.ac.uk> (University of Oxford, formerly University of Birmingham)
  //	
  //------------------------------------------------------------------------------
  //	
  //	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.ast;
  
  import param.BigRational;
  import parser.*;
  import parser.visitor.*;
  import prism.PrismLangException;
  import parser.type.*;
  public class ExpressionLiteral extends Expression
  {
  	Object value; // Value
  	String string; // Optionally, keep original string to preserve user formatting and allow exact evaluation
  
  	// Constructor
  	
  	public ExpressionLiteral(Type type, Object value)
  	{
  		this(type, value, ""+value);
  	}
  
  	public ExpressionLiteral(Type type, Object value, String string)
  	{
  		this.type = type;
  		this.value = value;
  		this.string = string;
  	}
  
  	// Set Methods
  	
  	public void setValue(Object value)
  	{
  		this.value = value;
  		this.string = ""+value;
  	}
  
  	public void setString(String string)
  	{
  		this.string = string;
  	}
  
  	// Get Methods
  	
  	public Object getValue()
  	{
  		return value;
  	}
  
  	public String getString()
  	{
  		return string;
  	}
  	
  	// Methods required for Expression:
  	
  	@Override
  	public boolean isConstant()
  	{
  		return true;
  	}
  
  	@Override
  	public boolean isProposition()
  	{
  		return true;
  	}
  	
  	@Override
  	public Object evaluate(EvaluateContext ec) throws PrismLangException
  	{
  		if (value instanceof BigRational) {
  			// cast from BigRational to appropriate Java data type
  			return getType().castFromBigRational((BigRational) value);
  		}
  		return value;
  	}
  
  	@Override
  	public BigRational evaluateExact(EvaluateContext ec) throws PrismLangException
  	{
  		if (value instanceof BigRational) {
  			// if already a BigRational, return that
  			return (BigRational) value;
  		} else if (value instanceof Boolean) {
  			return BigRational.from(value);
  		}
  		// otherwise, convert from string representation (potentially provides more precision for double literals)
  		return BigRational.from(string);
  	}
  
  	@Override
  	public boolean returnsSingleValue()
  	{
  		return true;
  	}
  
  	// Methods required for ASTElement:
  	
  	@Override
  	public Object accept(ASTVisitor v) throws PrismLangException
  	{
  		return v.visit(this);
  	}
  
  	@Override
  	public Expression deepCopy()
  	{
  		Expression expr = new ExpressionLiteral(type, value, string);
  		expr.setPosition(this);
  		return expr;
  	}
  
  	// Standard methods
  	
  	@Override
  	public String toString()
  	{
  		return string;
  	}
  
  	@Override
  	public int hashCode()
  	{
  		final int prime = 31;
  		int result = 1;
  		result = prime * result + ((string == null) ? 0 : string.hashCode());
  		result = prime * result + ((value == null) ? 0 : value.hashCode());
  		return result;
  	}
  
  	@Override
  	public boolean equals(Object obj)
  	{
  		if (this == obj)
  			return true;
  		if (obj == null)
  			return false;
  		if (getClass() != obj.getClass())
  			return false;
  		ExpressionLiteral other = (ExpressionLiteral) obj;
  		if (string == null) {
  			if (other.string != null)
  				return false;
  		} else if (!string.equals(other.string))
  			return false;
  		if (value == null) {
  			if (other.value != null)
  				return false;
  		} else if (!value.equals(other.value))
  			return false;
  		return true;
  	}
  }
  
  //------------------------------------------------------------------------------
  