I’m writing a quiz system using Elixir. Every time a user chooses an answer to a question, an %AnswerPacket{} struct is created, containing information on the answer. This packet is then processed by two GenServers, ScoreServer and AnswerServer, both of which have an update/2 function, taking the server pid and the packet.

Currently, I’m implementing this using GenEvent. There’s a third process, PacketHandler, that has a :push_packet event which forwards the packet to ScoreServer and AnswerServer, as below:

def handle_event({:push_packet, packet}, %{scores: scores, answers: answers} = pids)  do
  ScoreServer.update(scores, packet)
  AnswerServer.update(answers, packet)
  {:ok, pids}
end

This works pretty well, but I’m interested in how it could be reimplemented using GenStage. Am I right in thinking that PacketHandler would be the producer, and ScoreServer and AnswerServer consumers? If so, how would PacketHandler work? Currently the event is triggered by a function call, but the examples I’ve seen of GenStage seem more like a stream. And how does it fit in with the concept of demand, if its dependent on the user choosing an answer?

I’m a bit confused, so any help would be appreciated xD