private static bool TryTakeOperator(StringKeeper pos, out Token nextToken)
{
if (pos.NextIn(Operators))
{
var op = pos.Take();
nextToken = new OperatorToken(op);
return(true);
}
nextToken = null;
return(false);
}
private static bool TryTakeParens(StringKeeper pos, out Token nextToken)
{
if (pos.Next == '(')
{
var op = pos.Take();
nextToken = OpenParens;
return(true);
}
else if (pos.Next == ')')
{
var op = pos.Take();
nextToken = CloseParens;
return(true);
}
nextToken = null;
return(false);
}
private static bool TryTakeNumeric(StringKeeper pos, out Token nextToken)
{
var work = new StringKeeper(pos);
var number = string.Empty;
while (!work.Finished && work.NextIn("0123456789."))
{
number += work.Take();
}
if (number == string.Empty)
{
nextToken = null;
return(false);
}
var errorData = string.Empty;
while (!work.Finished && !work.WhiteSpaceNext() && !work.NextIn(Terminators))
{
errorData += work.Take();
}
if (!decimal.TryParse(number, out _) || errorData != string.Empty)
{
//we know that this is a badly formed number, so we should return an error token
nextToken = new ErrorToken(number + errorData, "Invalid number");
work.Swap(pos);
return(true);
}
if (number == string.Empty)
{
//if we didn't extract anything, this isn't a number at all.
nextToken = null;
return(false);
}
nextToken = new NumericToken(number);
work.Swap(pos);
return(true);
}
public static IEnumerable <Token> ExtractTokens(string input)
{
var pos = new StringKeeper(input);
pos.SkipWhiteSpace();
while (!pos.Finished)
{
Token nextToken = null;
if (TryTakeOperator(pos, out nextToken) ||
TryTakeNumeric(pos, out nextToken) ||
TryTakeParens(pos, out nextToken))
{
yield return(nextToken);
pos.SkipWhiteSpace();
continue;
}
yield return(new ErrorToken(pos, "Invalid token"));
break;
}
}
public StringKeeper(StringKeeper other)
{
_input = other._input;
_position = other._position;
}