std::variant matching and string representation

#include <iostream>
#include <variant>
#include <vector>

enum Brace { Round, Square };
enum Arity { Unary, Binary };
enum Assoc { Left, Right };
struct Op {
    char symbol;
    Arity ary;
    Assoc assoc;
    int prec;
};

struct Number { float n; };
struct RealVar { std::string v; };
struct BoolVar { std::string v; };
struct Operator { Op op; };
struct LeftParen { Brace b; };
struct RightParen { Brace b; };
struct Function { std::string f; };

using Token = std::variant<Number, RealVar, BoolVar, Operator, LeftParen, RightParen, Function>;

bool is_number(const Token& token) { return token.index() == 0; }
bool is_real_var(const Token& token) { return token.index() == 1; }
bool is_bool_var(const Token& token) { return token.index() == 2; }
bool is_operator(const Token& token) { return token.index() == 3; }
bool is_left_paren(const Token& token) { return token.index() == 4; }
bool is_right_paren(const Token& token) { return token.index() == 5; }
bool is_function(const Token& token) { return token.index() == 6; }

std::ostream& operator<< (std::ostream &os, const Op &op) {
    return os << "Op(" << op.symbol << "," << op.ary << "," << op.assoc << "," << op.prec << ")";
}

std::ostream& operator<< (std::ostream &os, const Token &token) {
    if (is_number(token)) return os << "Number(" << std::get<Number>(token).n << ")";
    else if (is_real_var(token)) return os << "RealVar(" << std::get<RealVar>(token).v << ")";
    else if (is_bool_var(token)) return os << "BoolVar(" << std::get<BoolVar>(token).v << ")";
    else if (is_operator(token)) return os << "Operator(" << std::get<Operator>(token).op << ")";
    else if (is_left_paren(token)) return os << "LeftParen(" << std::get<LeftParen>(token).b << ")";
    else if (is_right_paren(token)) return os << "RightParen(" << std::get<RightParen>(token).b << ")";
    else if (is_function(token)) return os << "Function(" << std::get<Function>(token).f << ")";
    else return os;
}

int main() {
    std::vector<Token> tokens = {
        Number { 0.123456 },
        RealVar { "Rsomething" },
        BoolVar { "Bflag" },
        Operator { Op { '+', Binary, Left, 5 } },
        LeftParen { Square },
        RightParen { Square },
        Function { "exp" }
    };
    // print all
    std::cout << "my tokens: \n";
    for (const auto& token : tokens) {
        std::cout << token << "\n";
    }

    std::cout << "\nHello, World!\n";
    return 0;
}