Y Combinator in C++20

ycomb.cpp

#include <iostream>

int main() {
    auto result = [](auto&& g) {
        return [](auto&& f) {
            return f(f);
        }([&g](auto&& f) { return g([&f](auto&& x) { return f(f)(x); }); });
    }([](auto&& f) {
        return [&f](auto&& x) -> int { return x == 0 ? 1 : x * f(x - 1); };
    })(5);

    std::cout << result << std::endl;
    return 0;
}