/// <summary>
/// Evaluates this expression.
/// </summary>
/// <returns></returns>
public override Token Evaluate()
{
Token result = new NullToken();
Token left = EvaluateOperand(1);
Token right = EvaluateOperand(0);
if (left is NumberToken && right is NumberToken)
{
double dLeft = 0.0;
double dRight = 0.0;
if (double.TryParse(left.ToString(), out dLeft) && double.TryParse(right.ToString(), out dRight))
{
if (Operation.ToString().Equals("==", StringComparison.InvariantCultureIgnoreCase))
{
result = new BooleanToken((dLeft == dRight).ToString());
}
else if (Operation.ToString().Equals("<=", StringComparison.InvariantCultureIgnoreCase))
{
result = new BooleanToken((dLeft <= dRight).ToString());
}
else if (Operation.ToString().Equals(">=", StringComparison.InvariantCultureIgnoreCase))
{
result = new BooleanToken((dLeft >= dRight).ToString());
}
else if (Operation.ToString().Equals("<", StringComparison.InvariantCultureIgnoreCase))
{
result = new BooleanToken((dLeft < dRight).ToString());
}
else if (Operation.ToString().Equals(">", StringComparison.InvariantCultureIgnoreCase))
{
result = new BooleanToken((dLeft > dRight).ToString());
}
else if (Operation.ToString().Equals("!=", StringComparison.InvariantCultureIgnoreCase))
{
result = new BooleanToken((dLeft != dRight).ToString());
}
else
{
throw new MalformedExpressionException(String.Format("Unknown boolean operator {0}.", Operation));
}
}
else
{
throw new FormatException(String.Format("Could not parse double value from {0} for boolean expression.", left.ToString()));
}
}
else if (left is BooleanToken && right is BooleanToken)
{
bool bLeft = false;
bool bRight = false;
if (bool.TryParse(left.ToString(), out bLeft) && bool.TryParse(right.ToString(), out bRight))
{
if (Operation.ToString().Equals("==", StringComparison.InvariantCultureIgnoreCase))
{
result = new BooleanToken((bLeft == bRight).ToString());
}
else if (Operation.ToString().Equals("!=", StringComparison.InvariantCultureIgnoreCase))
{
result = new BooleanToken((bLeft != bRight).ToString());
}
else
{
throw new MalformedExpressionException("Booleans cannot be less than or greater than each other.");
}
}
else
{
throw new FormatException(String.Format("Could not parse bool value from {0} for boolean expression.", left.ToString()));
}
}
else
{
throw new MalformedExpressionException(String.Concat(ToString(), " is not a valid boolean expression."));
}
return(result);
}
/// <summary>
/// Creates an instance of BooleanExpression.
/// </summary>
/// <param name="operation"></param>
/// <param name="left"></param>
/// <param name="right"></param>
public BooleanExpression(Token operation, Expression left, Expression right)
: base(ExpressionPrecedence.Boolean, operation, new List <Expression>() { left, right })
{
}