/// <summary>
/// Parses and extracts a symbol at the current position
/// </summary>
/// <param name="parser">TextParser object</param>
/// <returns></returns>
protected string ParseSymbolToken(TextParser parser)
{
int start = parser.Position;
while (Char.IsLetterOrDigit(parser.Peek()) || parser.Peek() == '_')
parser.MoveAhead();
return parser.Extract(start, parser.Position);
}
/// <summary>
/// Converts a standard infix expression to list of tokens in
/// postfix order.
/// </summary>
/// <param name="expression">Expression to evaluate</param>
/// <returns></returns>
protected List<string> TokenizeExpression(string expression)
{
List<string> tokens = new List<string>();
Stack<string> stack = new Stack<string>();
State state = State.None;
int parenCount = 0;
string temp;
TextParser 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 EvalException(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
parenCount++;
}
else if (parser.Peek() == ')')
{
// Must follow operand
if (state != State.Operand)
throw new EvalException(ErrOperandExpected, parser.Position);
// Must have matching open parenthesis
if (parenCount == 0)
throw new EvalException(ErrUnmatchedClosingParen, parser.Position);
// Pop all operators until matching "(" found
temp = stack.Pop();
while (temp != "(")
{
tokens.Add(temp);
temp = stack.Pop();
}
// Track number of parentheses
parenCount--;
}
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 EvalException(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 EvalException(ErrOperandExpected, parser.Position);
}
}
}
else if (Char.IsDigit(parser.Peek()) || parser.Peek() == '.')
{
if (state == State.Operand)
{
// Cannot follow other operand
throw new EvalException(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 EvalException(ErrOperatorExpected, parser.Position);
}
if (!(Char.IsLetter(parser.Peek()) || parser.Peek() == '_'))
{
// Invalid character
temp = String.Format(ErrUnexpectedCharacter, parser.Peek());
throw new EvalException(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 EvalException(ErrOperandExpected, parser.Position);
// Check for balanced parentheses
if (parenCount > 0)
throw new EvalException(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>
protected List<double> ParseParameters(TextParser parser)
{
// Move past open parenthesis
parser.MoveAhead();
// Look for function parameters
List<double> parameters = new List<double>();
parser.MovePastWhitespace();
if (parser.Peek() != ')')
{
// Parse function parameter list
int paramStart = parser.Position;
int parenCount = 1;
while (!parser.EndOfText)
{
if (parser.Peek() == ',')
{
// Note: Ignore commas inside parentheses. They could be
// from a parameter list for a function inside the parameters
if (parenCount == 1)
{
parameters.Add(EvaluateParameter(parser, paramStart));
paramStart = parser.Position + 1;
}
}
if (parser.Peek() == ')')
{
parenCount--;
if (parenCount == 0)
{
parameters.Add(EvaluateParameter(parser, paramStart));
break;
}
}
else if (parser.Peek() == '(')
{
parenCount++;
}
parser.MoveAhead();
}
}
// Make sure we found a closing parenthesis
if (parser.Peek() != ')')
throw new EvalException(ErrClosingParenExpected, parser.Position);
// Move past closing parenthesis
parser.MoveAhead();
// Return parameter list
return parameters;
}
/// <summary>
/// Parses and extracts a numeric value at the current position
/// </summary>
/// <param name="parser">TextParser object</param>
/// <returns></returns>
protected string ParseNumberToken(TextParser parser)
{
bool hasDecimal = false;
int start = parser.Position;
while (Char.IsDigit(parser.Peek()) || parser.Peek() == '.')
{
if (parser.Peek() == '.')
{
if (hasDecimal)
throw new EvalException(ErrMultipleDecimalPoints, parser.Position);
hasDecimal = true;
}
parser.MoveAhead();
}
// Extract token
string token = parser.Extract(start, parser.Position);
if (token == ".")
throw new EvalException(ErrInvalidOperand, parser.Position - 1);
return token;
}
/// <summary>
/// Extracts and evaluates a function parameter and returns its value. If an
/// exception occurs, it is caught and the column is adjusted to reflect the
/// position in original string, and the exception is rethrown.
/// </summary>
/// <param name="parser">TextParser object</param>
/// <param name="paramStart">Column where this parameter started</param>
/// <returns></returns>
protected double EvaluateParameter(TextParser parser, int paramStart)
{
try
{
// Extract expression and evaluate it
string expression = parser.Extract(paramStart, parser.Position);
return Execute(expression);
}
catch (EvalException ex)
{
// Adjust column and rethrow exception
ex.Column += paramStart;
throw ex;
}
}
/// <summary>
/// Evaluates a function and returns its value. It is assumed the current
/// position is at the opening parenthesis of the argument list.
/// </summary>
/// <param name="parser">TextParser object</param>
/// <param name="name">Name of function</param>
/// <param name="pos">Position at start of function</param>
/// <returns></returns>
protected double EvaluateFunction(TextParser parser, string name, int pos)
{
double result = default(double);
// Parse function parameters
List<double> parameters = ParseParameters(parser);
// We found a function reference
FunctionStatus status = FunctionStatus.UndefinedFunction;
if (ProcessFunction != null)
{
FunctionEventArgs args = new FunctionEventArgs();
args.Name = name;
args.Parameters = parameters;
args.Result = result;
args.Status = FunctionStatus.OK;
ProcessFunction(this, args);
result = args.Result;
status = args.Status;
}
if (status == FunctionStatus.UndefinedFunction)
throw new EvalException(String.Format(ErrUndefinedFunction, name), pos);
if (status == FunctionStatus.WrongParameterCount)
throw new EvalException(ErrWrongParamCount, pos);
return result;
}
/// <summary>
/// Converts a standard infix expression to list of tokens in
/// postfix order.
/// </summary>
/// <param name="expression">Expression to evaluate</param>
/// <returns></returns>
protected List <string> TokenizeExpression(string expression)
{
List <string> tokens = new List <string>();
Stack <string> stack = new Stack <string>();
State state = State.None;
int parenCount = 0;
string temp;
TextParser 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 EvalException(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
parenCount++;
}
else if (parser.Peek() == ')')
{
// Must follow operand
if (state != State.Operand)
{
throw new EvalException(ErrOperandExpected, parser.Position);
}
// Must have matching open parenthesis
if (parenCount == 0)
{
throw new EvalException(ErrUnmatchedClosingParen, parser.Position);
}
// Pop all operators until matching "(" found
temp = stack.Pop();
while (temp != "(")
{
tokens.Add(temp);
temp = stack.Pop();
}
// Track number of parentheses
parenCount--;
}
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 EvalException(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 EvalException(ErrOperandExpected, parser.Position);
}
}
}
else if (Char.IsDigit(parser.Peek()) || parser.Peek() == '.')
{
if (state == State.Operand)
{
// Cannot follow other operand
throw new EvalException(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 EvalException(ErrOperatorExpected, parser.Position);
}
if (!(Char.IsLetter(parser.Peek()) || parser.Peek() == '_'))
{
// Invalid character
temp = String.Format(ErrUnexpectedCharacter, parser.Peek());
throw new EvalException(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 EvalException(ErrOperandExpected, parser.Position);
}
// Check for balanced parentheses
if (parenCount > 0)
{
throw new EvalException(ErrClosingParenExpected, parser.Position);
}
// Retrieve remaining operators from stack
while (stack.Count > 0)
{
tokens.Add(stack.Pop());
}
return(tokens);
}
