I’ve created a custom GenServer macro, to abstract the logic from the user of a project I’m working on, Cadex. It’s used for modelling and simulating basic differential equation based models and eventually complex systems.

I’ve been experimenting with different ways I can create state update functions like below, and make it a bit cleaner - so the user only has to implement the core logic. Essentially I want to take the handle_call function and insert code before and after, adapt the function interface, but I’m struggling to get my head around it. You can see my WIP here: cadex/lib/cadex at robots-marbles-7 · BenSchZA/cadex · GitHub in decorators.ex and model.ex.

def handle_call(
        {:update, var},
        _from,
        state = %Cadex.Types.State{current: current, delta: delta}
      )
      when var == :box_A do
    increment =
      &(&1 +
          cond do
            current[var] > current[:box_B] -> -1
            current[var] < current[:box_B] -> 1
            true -> 0
          end)

    delta_ = %{var => increment}

    state_ =
      state
      |> Map.put(:delta, Map.merge(delta, delta_))

    {
      :reply,
      state_,
      state_
    }
  end

Rather something cleaner like this:

@state_update(:box_A)
def update_box_A(
        {:update, var},
        state = %Cadex.Types.State{current: current, delta: delta}
      ) do
    increment =
      &(&1 +
          cond do
            current[var] > current[:box_B] -> -1
            current[var] < current[:box_B] -> 1
            true -> 0
          end)

    {var: increment}
  end

In the GenServer macro, I’d then like to insert the rest of the code, and make sure the handle_call behaviour(?) is still implemented correctly and returns the right result. Is this possible?

I think I’ve messed around enough trying to implement a solution, and maybe some feedback would help me on my way! Appreciate any guidance