macro_fun.exs

defmodule MacroExp do
  defmacro attr_accessor(atom) do
    getter = String.to_atom("get_#{atom}")
    setter = String.to_atom("set_#{atom}")
    quote do
      def unquote(getter)(data) do
        data |> Map.from_struct |> Map.get(unquote(atom))
      end
      def unquote(setter)(data, value) do
        data |> Map.put(unquote(atom), value)
      end
    end
  end

  defmacro attr_reader(atom) do
    getter = String.to_atom("get_#{atom}")
    quote do
      def unquote(getter)(data) do
        data |> Map.from_struct |> Map.get(unquote(atom))
      end
    end
  end
end


defmodule Calculation do
  import MacroExp
  defstruct first: nil, second: nil, operator: :plus

  attr_accessor :first   # defines set_first/2 and get_first/1
  attr_accessor :second  # defines set_second/2 and get_second/1
  attr_reader :operator  # defines set_operator/2 and get_operator/1

  def result(%Calculation{first: first, second: second, operator: :plus}) do
    first + second
  end
end