public virtual void parse(string expression)
{
// Save the expression.
bool parse = true;
if (!expression.Equals(previousExpression))
{
previousExpression = expression;
}
else
{
parse = false;
operatorStack = (Stack)previousOperatorStack.Clone();
operandStack = (Stack)previousOperandStack.Clone();
}
try
{
if (parse)
{
operandStack = new Stack();
operatorStack = new Stack();
bool haveOperand = false;
bool haveOperator = false;
Operator unaryOperator = null;
int numChars = expression.Length;
int charCtr = 0;
while (charCtr < numChars)
{
Operator @operator = null;
int operatorIndex = -1;
if (EvaluationHelper.isSpace(expression[charCtr]))
{
charCtr++;
continue;
}
NextOperator nextOperator = getNextOperator(expression, charCtr, null);
if (nextOperator != null)
{
@operator = nextOperator.Operator;
operatorIndex = nextOperator.Index;
}
if (operatorIndex > charCtr || operatorIndex == -1)
{
charCtr = processOperand(expression, charCtr, operatorIndex, operandStack, unaryOperator);
haveOperand = true;
haveOperator = false;
unaryOperator = null;
}
// Check if it is time to process an operator.
if (operatorIndex == charCtr)
{
if (nextOperator.Operator.Unary && (haveOperator || charCtr == 0))
{
charCtr = processUnaryOperator(operatorIndex, nextOperator.Operator);
if (unaryOperator == null)
{
// We have an unary operator.
unaryOperator = nextOperator.Operator;
}
else
{
throw new EvaluationException("Consecutive unary " + "operators are not allowed (index=" + charCtr + ").");
}
}
else
{
charCtr = processOperator(expression, operatorIndex, @operator, operatorStack, operandStack, haveOperand, unaryOperator);
unaryOperator = null;
}
if (!(nextOperator.Operator is ClosedParenthesesOperator))
{
haveOperand = false;
haveOperator = true;
}
}
}
// Save the parsed operators and operands.
previousOperatorStack = (Stack)operatorStack.Clone();
previousOperandStack = (Stack)operandStack.Clone();
}
}
catch (Exception e)
{
// Clear the previous expression, because it is invalid.
previousExpression = "";
throw new EvaluationException(e.Message, e);
}
}