//==============================================================================
//	
//	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 parser.*;
import parser.visitor.*;
import prism.PrismLangException;

public class ExpressionITE extends Expression
{
	// Operands
	protected Expression operand1 = null; // condition
	protected Expression operand2 = null; // then
	protected Expression operand3 = null; // else

	// Constructor

	public ExpressionITE(Expression c, Expression t, Expression e)
	{
		operand1 = c;
		operand2 = t;
		operand3 = e;
	}

	// Set methods

	public void setOperand1(Expression e)
	{
		operand1 = e;
	}

	public void setOperand2(Expression e)
	{
		operand2 = e;
	}

	public void setOperand3(Expression e)
	{
		operand3 = e;
	}

	// Get methods

	public Expression getOperand1()
	{
		return operand1;
	}

	public Expression getOperand2()
	{
		return operand2;
	}

	public Expression getOperand3()
	{
		return operand3;
	}

	// Methods required for Expression:

	/**
	 * Is this expression constant?
	 */
	public boolean isConstant()
	{
		return operand1.isConstant() && operand2.isConstant() && operand3.isConstant();
	}

	@Override
	public boolean isProposition()
	{
		return operand1.isProposition() && operand2.isProposition() && operand3.isProposition();
	}
	
	/**
	 * Evaluate this expression, return result. Note: assumes that type checking
	 * has been done already.
	 */
	public Object evaluate(EvaluateContext ec) throws PrismLangException
	{
		return operand1.evaluateBoolean(ec) ? operand2.evaluate(ec) : operand3.evaluate(ec);
	}

	@Override
	public boolean returnsSingleValue()
	{
		return operand1.returnsSingleValue() && operand2.returnsSingleValue() && operand3.returnsSingleValue();
	}

	// Methods required for ASTElement:

	/**
	 * Visitor method.
	 */
	public Object accept(ASTVisitor v) throws PrismLangException
	{
		return v.visit(this);
	}

	/**
	 * Convert to string.
	 */
	public String toString()
	{
		return operand1 + " ? " + operand2 + " : " + operand3;
	}

	/**
	 * Perform a deep copy.
	 */
	public Expression deepCopy()
	{
		ExpressionITE expr = new ExpressionITE(operand1.deepCopy(), operand2.deepCopy(), operand3.deepCopy());
		expr.setType(type);
		expr.setPosition(this);
		return expr;
	}
}

// ------------------------------------------------------------------------------
