iex - Missing stacktrace

stack_pls.ex

defmodule StackPls do
  @behaviour :gen_statem

  def callback_mode(), do: :state_functions

  def start_link(opts) do
     :gen_statem.start_link(__MODULE__, opts, [])
  end

  # Mandatory callback functions

  def code_change(_old_vsn, old_state, old_data, _extra) do
    {callback_mode(), old_state, old_data}
  end

  def terminate(_reason, _state, _data), do: :void

  def nest(m, 0) do Map.put(m, :foo, 0) end

  def nest(m, depth_left) do
    child = Enum.reduce([:foo, :bar, :baz, :ac, :dc, :yelp, :smart, "wait"], %{}, fn(k, acc) -> Map.put(acc, k, nest(%{}, depth_left - 1)) end)
    Map.put(m, :child, child)
  end

  def init(opts) do
    start_data = nest(%{}, 5)
    tref = :erlang.start_timer(200, self(), :wait_for_it)
    {callback_mode(), :starting, start_data}
  end

  def starting(:info, _, data) do
    {:bad_pattern, a, b, c} = data
    {:keep_state, data}
  end
end