auto operator()() const {

const auto guard = [] { return true; };

const auto action = [](int &a) { ++a; };

// clang-format off

using namespace sml;

using sml::eval;

return make_transition_table(

*"idle"_s + event<e1> [ guard ] / (action, eval [ guard ] / action, action) = X

);

// clang-format on

}

int a{};

sml::sm<eval> sm{a};

sm.process_event(e1{});

assert(3 == a);

assert(sm.is(sml::X));