https://www.codewars.com/kata/55bf01e5a717a0d57e0000ec/train/elixir

persistent_bugger.ex

defmodule PersistentBugger do
  @moduledoc """
  Calculate multiplicative persistence.
  https://www.codewars.com/kata/persistent-bugger/train/elixir
  """

  def persistence(num, count \\ 0) when num < 10, do: count
  def persistence(num, count \\ 0) do
    num
    |> Integer.digits
    |> multiply
    |> do_persistence(count + 1)
  end
  
  defp multiply([i | n]), do: Enum.reduce(n, i, &(&1 * &2))
end