/// <summary>
/// Converts a standard infix expression to list of tokens in
/// postfix order.
/// </summary>
/// <param name="expression">Expression to evaluate</param>
/// <returns></returns>
private List <string> TokenizeExpression(string expression)
{
var tokens = new List <string>();
var stack = new Stack <string>();
var state = State.None;
int parenDepth = 0;
string temp;
var parser = new TextParser(expression);
while (!parser.EndOfText)
{
if (char.IsWhiteSpace(parser.Peek()))
{
// ignore spaces, tabs, etc.
}
else if (parser.Peek() == '(')
{
// cannot follow operand
if (state == State.Operand)
{
throw new FormulaException(ErrOperatorExpected, parser.Position);
}
// Allow additional unary operators after "("
if (state == State.UnaryOperator)
{
state = State.Operator;
}
// push opening parenthesis onto stack
stack.Push(parser.Peek().ToString());
// track number of parentheses
parenDepth++;
}
else if (parser.Peek() == ')')
{
// Must follow operand
if (state != State.Operand)
{
throw new FormulaException(ErrOperandExpected, parser.Position);
}
// Must have matching open parenthesis
if (parenDepth == 0)
{
throw new FormulaException(ErrUnmatchedClosingParen, parser.Position);
}
// Pop all operators until matching "(" found
temp = stack.Pop();
while (temp != "(")
{
tokens.Add(temp);
temp = stack.Pop();
}
// Track number of parentheses
parenDepth--;
}
else if ("+-*/^".Contains(parser.Peek()))
{
// Need a bit of extra code to support unary operators
if (state == State.Operand)
{
// Pop operators with precedence >= current operator
int currPrecedence = GetPrecedence(parser.Peek().ToString());
while (stack.Count > 0 && GetPrecedence(stack.Peek()) >= currPrecedence)
{
tokens.Add(stack.Pop());
}
stack.Push(parser.Peek().ToString());
state = State.Operator;
}
else if (state == State.UnaryOperator)
{
// Don't allow two unary operators together
throw new FormulaException(ErrOperandExpected, parser.Position);
}
else
{
// Test for unary operator
if (parser.Peek() == '-')
{
// Push unary minus
stack.Push(UnaryMinus);
state = State.UnaryOperator;
}
else if (parser.Peek() == '+')
{
// Just ignore unary plus
state = State.UnaryOperator;
}
else
{
throw new FormulaException(ErrOperandExpected, parser.Position);
}
}
}
else if (char.IsDigit(parser.Peek()) || parser.Peek() == '.')
{
if (state == State.Operand)
{
// Cannot follow other operand
throw new FormulaException(ErrOperatorExpected, parser.Position);
}
// Parse number
temp = ParseNumberToken(parser);
tokens.Add(temp);
state = State.Operand;
continue;
}
else
{
double result;
// Parse symbols and functions
if (state == State.Operand)
{
// Symbol or function cannot follow other operand
throw new FormulaException(ErrOperatorExpected, parser.Position);
}
if (!(char.IsLetter(parser.Peek()) || parser.Peek() == '_'))
{
// Invalid character
temp = string.Format(ErrUnexpectedCharacter, parser.Peek());
throw new FormulaException(temp, parser.Position);
}
// save start of symbol for error reporting
int symbolPos = parser.Position;
// parse this symbol
temp = ParseSymbolToken(parser);
// skip whitespace
parser.MovePastWhitespace();
// check for parameter list
if (parser.Peek() == '(')
{
// found parameter list, evaluate function
result = EvaluateFunction(parser, temp, symbolPos);
}
else
{
// no parameter list, evaluate symbol (variable)
result = EvaluateSymbol(temp, symbolPos);
}
// handle negative result
if (result < 0)
{
stack.Push(UnaryMinus);
result = Math.Abs(result);
}
tokens.Add(result.ToString());
state = State.Operand;
continue;
}
parser.MoveAhead();
}
// Expression cannot end with operator
if (state == State.Operator || state == State.UnaryOperator)
{
throw new FormulaException(ErrOperandExpected, parser.Position);
}
// Check for balanced parentheses
if (parenDepth > 0)
{
throw new FormulaException(ErrClosingParenExpected, parser.Position);
}
// Retrieve remaining operators from stack
while (stack.Count > 0)
{
tokens.Add(stack.Pop());
}
return(tokens);
}
/// <summary>
/// Evaluates each parameter of a function's parameter list and returns
/// a list of those values. An empty list is returned if no parameters
/// were found. It is assumed the current position is at the opening
/// parenthesis of the argument list.
/// </summary>
/// <param name="parser">TextParser object</param>
/// <returns></returns>
private List <double> ParseParameters(TextParser parser)
{
// Move past open parenthesis
parser.MoveAhead();
// Look for function parameters
var parameters = new List <double>();
parser.MovePastWhitespace();
if (parser.Peek() != ')')
{
// Parse function parameter list
int paramStart = parser.Position;
int pardepth = 1;
while (!parser.EndOfText)
{
if (parser.Peek() == ':')
{
// assume current token and next token are cell references
var p1 = parser.Position;
var cell1 = parser.Extract(paramStart, parser.Position);
parser.MoveAhead();
var p2 = parser.Position;
var cell2 = ParseSymbolToken(parser);
paramStart = parser.Position;
parameters.AddRange(EvaluateCellReferences(cell1, cell2, p1, p2));
}
else if (parser.Peek() == ',')
{
// Note: Ignore commas inside parentheses. They could be
// from a parameter list for a function inside the parameters
if (pardepth == 1)
{
parameters.Add(EvaluateParameter(parser, paramStart));
paramStart = parser.Position + 1;
}
}
if (parser.Peek() == ')')
{
pardepth--;
if (pardepth == 0)
{
if (paramStart < parser.Position)
{
parameters.Add(EvaluateParameter(parser, paramStart));
}
break;
}
}
else if (parser.Peek() == '(')
{
pardepth++;
}
parser.MoveAhead();
}
}
// Make sure we found a closing parenthesis
if (parser.Peek() != ')')
{
throw new FormulaException(ErrClosingParenExpected, parser.Position);
}
// Move past closing parenthesis
parser.MoveAhead();
// Return parameter list
return(parameters);
}
