/// <summary>
/// Parses and extracts a numeric value at the current position.
/// </summary>
/// <param name="parser">Current parsing helper object.</param>
/// <returns>The extracted number token string.</returns>
private Variable ParseNumber(ParsingHelper parser)
{
Debug.Assert(IsNumberChar(parser.Peek()));
bool hasDecimal = false;
int start = parser.Index;
while (char.IsDigit(parser.Peek()) || parser.Peek() == '.')
{
if (parser.Peek() == '.')
{
if (hasDecimal)
{
throw new ExpressionException(ErrMultipleDecimalPoints, parser.Index);
}
hasDecimal = true;
}
parser++;
}
// Extract token
string token = parser.Extract(start, parser.Index);
if (token == ".")
{
throw new ExpressionException(ErrInvalidOperand, parser.Index - 1);
}
if (hasDecimal)
{
return(new Variable(double.Parse(token)));
}
return(new Variable(int.Parse(token)));
}
/// <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">ParsingHelper object.</param>
/// <returns>A list of parameter values.</returns>
private Variable[] ParseParameters(ParsingHelper parser)
{
List <Variable> parameters = new();
// Move past open parenthesis
parser++;
parser.SkipWhiteSpace();
// If function has any parameters
if (parser.Peek() != ')')
{
// Parse function parameter list
int start = parser.Index;
int parenCount = 1;
while (!parser.EndOfText)
{
if (parser.Peek() == ',')
{
// Note: Ignore commas inside parentheses. They could be
// for a parameter list in a function inside the parameters
if (parenCount == 1)
{
parameters.Add(ParseParameter(parser, start));
start = parser.Index + 1;
}
}
if (parser.Peek() == ')')
{
parenCount--;
if (parenCount == 0)
{
parameters.Add(ParseParameter(parser, start));
break;
}
}
else if (parser.Peek() == '(')
{
parenCount++;
}
parser++;
}
}
// Make sure we found a closing parenthesis
if (parser.Peek() != ')')
{
throw new ExpressionException(ErrClosingParenExpected, parser.Index);
}
// Move past closing parenthesis
#pragma warning disable IDE0059 // Unnecessary assignment of a value
parser++;
#pragma warning restore IDE0059 // Unnecessary assignment of a value
// Return parameter list
return(parameters.ToArray());
}
/// <summary>
/// Converts a standard infix expression to list of tokens in
/// postfix order.
/// </summary>
/// <param name="expression">Expression to evaluate.</param>
/// <returns>List of tokens in postfix order.</returns>
private List <IToken> TokenizeExpression(string expression)
{
ParsingHelper parser = new ParsingHelper(expression);
List <IToken> tokens = new List <IToken>();
Stack <IToken> stack = new Stack <IToken>();
State state = State.None;
int parenCount = 0;
IToken token;
while (true)
{
parser.SkipWhiteSpace();
if (parser.EndOfText)
{
break;
}
// Get next character
char c = parser.Peek();
if (c == '(')
{
// Cannot follow operand
if (state == State.Operand)
{
throw new ExpressionException(ErrOperatorExpected, parser.Index);
}
// Allow additional unary operators after "("
if (state == State.UnaryOperator)
{
state = State.Operator;
}
// Push opening parenthesis onto stack
stack.Push(new LeftParenthesisToken());
// Track number of parentheses
parenCount++;
}
else if (c == ')')
{
// Must follow operand
if (state != State.Operand)
{
throw new ExpressionException(ErrOperandExpected, parser.Index);
}
// Must have matching open parenthesis
if (parenCount == 0)
{
throw new ExpressionException(ErrUnmatchedClosingParen, parser.Index);
}
// Pop all operators until matching "(" found
token = stack.Pop();
while (token.Type != TokenType.LeftParenthesis)
{
tokens.Add(token);
token = stack.Pop();
}
// Track number of parentheses
parenCount--;
}
else if (OperatorToken.GetOperatorInfo(c, out OperatorInfo info))
{
// Need a bit of extra code to support unary operators
if (state == State.Operand)
{
// Pop operators with precedence >= current operator
while (stack.Count > 0 && stack.Peek().Precedence >= info.Precedence)
{
tokens.Add(stack.Pop());
}
stack.Push(new OperatorToken(info));
state = State.Operator;
}
else if (state == State.UnaryOperator)
{
// Don't allow two unary operators together
throw new ExpressionException(ErrOperandExpected, parser.Index);
}
else
{
// Test for unary operator
if (c == '-')
{
// Push unary minus
stack.Push(new OperatorToken(OperatorToken.OpNegate));
state = State.UnaryOperator;
}
else if (c == '+')
{
// Just ignore unary plus
state = State.UnaryOperator;
}
else
{
throw new ExpressionException(ErrOperandExpected, parser.Index);
}
}
}
else if (IsNumberChar(c))
{
if (state == State.Operand)
{
// Cannot follow other operand
throw new ExpressionException(ErrOperatorExpected, parser.Index);
}
// Parse number
tokens.Add(new OperandToken(ParseNumber(parser)));
state = State.Operand;
continue;
}
else if (IsSymbolFirstChar(c))
{
// Parse symbols and functions
if (state == State.Operand)
{
// Symbol or function cannot follow other operand
throw new ExpressionException(ErrOperatorExpected, parser.Index);
}
// Save start of symbol for error reporting
int symbolPos = parser.Index;
// Parse this symbol
string symbol = parser.ParseWhile(IsSymbolChar);
// Skip whitespace
parser.SkipWhiteSpace();
// Check for parameter list
Variable result;
if (parser.Peek() == '(')
{
// Found parameter list, evaluate function
result = ParseFunction(parser, symbol, symbolPos);
}
else
{
// No parameter list, evaluate symbol (variable)
result = ParseSymbol(symbol, symbolPos);
}
tokens.Add(new OperandToken(result));
state = State.Operand;
// Don't MoveAhead again
continue;
}
else if (c == '"' || c == '\'')
{
// String literal
string text = parser.ParseQuotedText();
tokens.Add(new OperandToken(new Variable(text)));
state = State.Operand;
}
else
{
// Unrecognized character
throw new ExpressionException(ErrUnexpectedCharacter, c, parser.Index);
}
parser++;
}
// Expression cannot end with operator
if (state == State.Operator || state == State.UnaryOperator)
{
throw new ExpressionException(ErrOperandExpected, parser.Index);
}
// Check for balanced parentheses
if (parenCount > 0)
{
throw new ExpressionException(ErrClosingParenExpected, parser.Index);
}
// Retrieve remaining operators from stack
while (stack.Count > 0)
{
tokens.Add(stack.Pop());
}
return(tokens);
}