Pascal Version

 const
    ParseRegexPattern: String = '(?<Sign>[+-]?)((?<BaseHex>\$)|(?<BaseOct>0))?';
    var
        ParseRegex: TRegEx;
        sMatch: TMatch;
        numberBase: UInt32;
        checkFormat: Boolean;
  begin

ParseRegex := TRegEx.Create(ParseRegexPattern, [roCompiled]);

   if (sMatch.Groups['Sign'].Value = '-') then
    begin
      negative := True;
    end;

     if (smatch.Groups['BaseHex'].Length <> 0) then
    begin
      if (checkFormat) then
      begin
        // $ before the number - this is hex number
        numberBase := UInt32(16);
      end
      else
      begin
        // This is an error
        raise Exception.Create(Strings.ParseInvalidChar);
      end
    end

    else

 if (smatch.Groups['BaseOct'].Length <> 0) then
    begin
      if (checkFormat) then
      begin
        // 0 before the number - this is octal number
        numberBase := UInt32(8);
      end;

      stringNotEmpty := True;
    end;

   end;