a bunch of recursive functions based on the little elixir and OTP book

recursion_examples.ex

defmodule Mods do
  def list_len(list) do
    list_len(0, list)
  end

  defp list_len(acc, []), do: acc
  defp list_len(acc, [_h|t]) do
    list_len((acc + 1), t)
  end

  def range(from, to) do
    range([], to, from)
  end

  defp range(acc, to, to), do: acc |> Enum.reverse
  defp range(acc, to, from) do
    range([from | acc], to, (from + 1))
  end

  def positive(list) do
    positive([], list)
  end

  def positive(acc, []), do: acc |> Enum.reverse
  def positive(acc, [h|t]) when h >= 0 do
    positive([h | acc], t)
  end
  def positive(acc, [h|t]) when h < 0 do
    positive(acc, t)
  end
end