Elixir - Body-recursion vs Tail-Recursion for Fibonacci

fibonacci.ex

# Body-recursive
#
# Note: "+" is actually the last call, not calculate/1.
defmodule Fibonacci do
  def calculate(x) when x <= 2, do: 1
  def calculate(x), do: calculate(x - 1) + calculate(x - 2)
end

# Tail-recursive (Tail Call Optimization)
#
# Note: tail-recursion is triggered since do_calculate/3 calls itself
#       at the very end of the function.
defmodule FibonacciTCO do
  def calculate(x), do: do_calculate(0, 1, x)
  def do_calculate(_, result, 1), do: result
  def do_calculate(a, b, x), do: do_calculate(b, a + b, x - 1)
end

Fibonacci.calculate(40) |> IO.puts
FibonacciTCO.calculate(40) |> IO.puts