I'm surprised nobody mentioned co_await yet. This should be possible.

std::optional<int> foo();

And then

std::optional<int> bar(){

   int x = co_await foo();

   int y = co_await foo();

   return x+y;

}

No messy chaining or lambda pyramid of doom.

I'm surprised that the monadic ops and C++ co_await are not being aligned in the standard yet