MyMath, functions that are traced by ReconTrace

my_math.ex

defmodule MyMath do

  @spec factorial(non_neg_integer()) :: non_neg_integer()
  def factorial(0),             do: 1
  def factorial(n) when n > 0,  do: n * factorial(n - 1)

  @spec factorial_iter(non_neg_integer()) :: non_neg_integer()
  def factorial_iter(n) when n >= 0, do: factorial_iter1(n, 1)

  defp factorial_iter1(0, acc), do: 1   # `1` should read `acc`
  defp factorial_iter1(n, acc), do: factorial_iter1(n - 1, acc * n)

  @spec permutations([term()]) :: [[term()]]
  def permutations([]) do
    [[]]
  end

  def permutations(items) when is_list(items) do
    for head <- items, tail <- permutations(items -- [head]) do
      [head | tail]
    end
  end

end