Concurrent Data Processing in Elixir: Using a mapper operation after reduce/3 is deprecated (page 114)

@svilen

warning: Using a mapper operation, such as map/filter/reject, after reduce/3 is deprecated. Use Flow.on_trigger/2 instead
(flow 1.2.0) lib/flow.ex:1916: Flow.add_mapper/3
(airports 0.1.0) lib/airports.ex:25: Airports.open_airports/0
(stdlib 4.0.1) erl_eval.erl:744: :erl_eval.do_apply/7
(elixir 1.13.4) src/elixir.erl:296: :elixir.recur_eval/3
(elixir 1.13.4) src/elixir.erl:274: :elixir.eval_forms/3
(iex 1.13.4) lib/iex/evaluator.ex:310: IEx.Evaluator.handle_eval/3

How would we rewrite this as an on_trigger function?