Elixir: Fibonacci

fibonacci.ex

defmodule Fibonacci do
  @moduledoc """
  In mathematics, the Fibonacci numbers are the numbers in the following
  integer sequence, called the Fibonacci sequence, and characterized by the
  fact that every number after the first two is the sum of the two preceding
  ones.
  """

  @doc """
  Finds the nth fibonacci number.
  """
  def nth(0), do: 0
  def nth(1), do: 1
  def nth(n) do
    nth(n - 1) + nth(n - 2)
  end
end

iex

iex(1)> c "fibonacci.ex"
[Fibonacci]
iex(2)> Fibonacci.nth 7
13
iex(3)> Fibonacci.nth 15
610
iex(4)> Fibonacci.nth 20
6765
iex(5)> Fibonacci.nth 25
75025