code: function fibonacci() {
      return defer(function* () {
          let prev = 1;
          let curr = 1;
          yield prev;
          yield curr;
          for (;;) {
              let temp = prev;
              prev = curr;
              curr = temp + curr;
              yield curr;
          }
      });
  }
docs: Yields the infinite fibonacci sequence (1, 1, 2, 3, 5, 8, 13, etc...)