#define deferasync(fun) async(fun, deferred)
#define LAMBDA []()

//cout << "a"; yield 1; cout << "b"; yield 2; cout << "c";
auto generator =
  deferasync(LAMBDA {
               cout<<"a";
               return pair{1, deferasync(LAMBDA {
                                           cout << "b";
                                           return pair{2, deferasync(LAMBDA {
                                                                       cout << "c";
                                                                     })
                                         })};
             });