defmodule Tr do
  @moduledoc """
  A demo of tail recursion vs no tail recursion to do the same task
  for 1000000000, the tr version took 3 seconds on my mac
  the non-tr version I gave up on.
  """

  @doc """
  Non tail recursive implementation of summing to a number
  Works fine as long as the number is small
  """
  def sum_to_n(0) do
    0
  end
  def sum_to_n(n) do
    n+sum_to_n(n-1)
  end

  @doc """
  The tail recursive version of summing.
  TR usually requires passing along extra parameters.
  Here,
  """
  def tr_sum_to_n(n) do
    tr_sum_to_n(n, 0)
  end
  def tr_sum_to_n(0, sum) do
    sum
  end
  def tr_sum_to_n(n, sum) do
    tr_sum_to_n(n-1, sum+n)
  end
end

#IO.puts Tr.sum_to_n(10000000)
IO.puts Tr.tr_sum_to_n(10000000)