Fibonacci sequence in Elixir

fibonacci.ex

defmodule Fibonacci do
  def find(nth) do
    list = [1, 1]
    fib(list, nth)
  end

  def fib(list, 2) do
    Enum.reverse(list)
  end

  def fib(list, n) do
    fib([hd(list) + hd(tl(list))] ++ list, n - 1)
  end
end

# Usage:
# > find 7
# [1, 1, 2, 3, 5, 8, 13]

If you construct the Fibonacci sequence as a list, and construct it in reverse, Elixir's built-in head and tail functions make it easy to compute with tail-call optimization for free.