class Token {
    string Str;
    int StartIndex;
    int Length;
    // It is not a enum because there is no way to convert enum value to int in Fusion.
    // The Type is also the priority of the token in calculation (see Parser).
    int Type;
    
    public const int Type_Literal=11;
    public const int Type_OperatorPow=10;
    public const int Type_OperatorMul=9;
    public const int Type_OperatorMod=8;
    public const int Type_OperatorDiv=7;
    public const int Type_OperatorAdd=6;
    public const int Type_OperatorSub=5;
    public const int Type_BracketOpen=3;
    public const int Type_BracketClose=2;
    public const int Type_Number=1;

    internal static Token() Create(string str, int startIndex, int length, int type){
        Token() tok = {
            Str = str,
            StartIndex = startIndex,
            Length = length,
            Type = type
        };
        return tok;
    }

    internal string() GetStr() => Str.Substring(StartIndex, Length);
    internal int GetTokType() => Type;
}