Builder pattern in Elixir (don't do this!!!)

nice_pattern.exs

defmodule Person do
  defstruct [:name, :age]

  def with do
    {Person.Builder, %{}}
  end

  defmodule Builder do
    def unquote(:'$handle_undefined_function')(:and_with, [{__MODULE__, _acc} = tuple]) do
      tuple
    end

    def unquote(:'$handle_undefined_function')(attr, [value, {__MODULE__, acc}]) do
      {__MODULE__, Map.put(acc, attr, value)}
    end

    def build!({__MODULE__, attrs}) do
      struct!(Person, attrs)
    end
  end
end

person = Person
  .with.name("John")
  .and_with.age(35)
  .build!()

IO.inspect(person) #=> %Person{age: 35, name: "John"}