std::unordered_map<std::string, tokentype> keywords = {
    { "Ohai", TokenType::Ohai }
};

// For tokens which are always exactly one character
std::unordered_map<char, tokentype> punctuation = {
    { '}', TokenType::CloseCurlyBrace },
    { '{', TokenType::OpenCurlyBrace },
};

struct Token {
    TokenType t;
    Token(TokenType type) : t(type) {}
};

std::vector<Token> lex(std::string s) {
    std::vector<Token> out;

    for(auto it = s.begin(); it != s.end(); ++it) {
        auto next = [&] { return *(it + 1); };

        auto single_equals = [&](char c, TokenType single, TokenType equals) -> bool {
            if (*it == c) {
                if (next() == '=') {
                    out.push_back(equals);
                    ++it;
                    return true;
                }
                out.push_back(single);
                return true;
            }
            return false;
        };

        auto double_equals = [&](char c, TokenType single, TokenType double, TokenType equals) -> bool {
            if (*it == c) {
                if (next() == '=') {
                    out.push_back(equals);
                    ++it;
                    return true;
                }
                if (next() == c) {
                    out.push_back(double);
                    ++it;
                    return true;
                }
                out.push_back(single);
                return true;
            }
            return false;
        };

        if (*it == '/') {
            if (next() == '/') {
                while(*it != '\n') {
                    ++it;
                ++it;
                continue;
            }
            if (next() == '*') {
                while(*it != '*') {
                    ++it;
                    if (next() == '/')
                        ++it;
                        break;
                    }
                }
                continue;
            }
        }

        if (punctuation.find(*it) != punctuation.end()) {
            out.push_back(punctuation[*it]);
            ++it;
            continue;
        }
        if (single_equals('/', TokenType::Div, TokenType::DivEquals)) continue;
        if (single_equals('!', TokenType::Not, TokenType::NotEquals)) continue;
        if (double_equals('+', TokenType::Plus, TokenType::Increment, TokenType::PlusEquals)) continue;
        if (double_equals('-', TokenType::Sub, TokenType::Decrement, TokenType::SubEquals)) continue;
    }
    return out;
}