public void ReduceRoot()
{
if (this.Tokens.Count == 1)
{
Token token = this.LastToken;
// Delete naked groups
if (token is PartialCompletedExpression g)
{
this.Tokens.Clear();
this.Tokens.AddRange(g.Tokens);
}
// Artificially insert a bogus operator for values
if (token is ValueToken)
{
this.AddToken(OperatorToken.CreateFromString("*", -1));
this.AddToken(ValueToken.Create(1, -1));
}
}
}
private static List <Token> Tokenize(string expression)
{
Stack <ParsingContext> parsingContextStack = new Stack <ParsingContext>();
ParsingContext parsingContext = new ParsingContext();
int index;
void CompleteNumber()
{
StringBuilder currentToken = parsingContext.CurrentToken;
if (currentToken.Length > 0)
{
parsingContext.AddToken(ValueToken.CreateFromString(currentToken.ToString(), index));
}
currentToken.Clear();
}
void CompleteMinusExpression(bool isOperator)
{
if (parsingContext.PossiblePendingOperator != '-')
{
return;
}
if (isOperator)
{
parsingContext.AddToken(
OperatorToken.CreateFromString("-", index + 1)
);
parsingContext.PossiblePendingOperator = Char.MinValue;
return;
}
if (parsingContext.LastToken is PartialCompletedExpression g)
{
List <Token> tokenList = new List <Token>
{
ValueToken.CreateFromString("-1", index),
OperatorToken.CreateFromString("*", index),
g
};
// Last is a group, and "-(1 * 3)" is actually "-1 * (1 * 3)"
parsingContext.ReplaceToken(
parsingContext.LastToken,
PartialCompletedExpression.Create(
tokenList
)
);
}
else if (parsingContext.LastToken is ValueToken vt)
{
parsingContext.ReplaceToken(
parsingContext.LastToken,
ValueToken.Create(-1 * vt.Value, vt.Position)
);
}
else
{
parsingContext.AppendToPartiallyCompletedToken(parsingContext.PossiblePendingOperator);
}
parsingContext.PossiblePendingOperator = Char.MinValue;
}
// Parse token from right to left
for (index = expression.Length - 1; index >= 0; index--)
{
char ch = expression[index];
// Whitespace does not matter
if (Char.IsWhiteSpace(ch))
{
continue;
}
// Group take precedence
if (ch == ')')
{
CompleteNumber();
CompleteMinusExpression(true);
parsingContextStack.Push(parsingContext);
parsingContext = new ParsingContext();
continue;
}
// Group end
if (ch == '(')
{
CompleteMinusExpression(false);
CompleteNumber();
ParsingContext groupContext = parsingContext;
parsingContext = parsingContextStack.Pop();
parsingContext.AddToken(
PartialCompletedExpression.Create(groupContext.Tokens)
);
continue;
}
if (ch == '-')
{
// Otherwise it is probably part of a number, so just prepend it
CompleteNumber();
if (parsingContext.PossiblePendingOperator == ch)
{
CompleteMinusExpression(false);
}
parsingContext.PossiblePendingOperator = ch;
continue;
}
if (Char.IsDigit(ch) || ch == '.')
{
CompleteMinusExpression(true);
parsingContext.AppendToPartiallyCompletedToken(ch);
}
else
{
CompleteMinusExpression(false);
CompleteNumber();
parsingContext.AddToken(OperatorToken.CreateFromString(ch.ToString(), index));
}
}
CompleteNumber();
CompleteMinusExpression(false);
parsingContext.ReduceRoot();
return(parsingContext.Tokens);
}