A quick example of Fibbonaci sequence using Elixir's Stream (unlike eager Enums, Streams are lazy, generated 1 by 1 during execution, and highly composable)

fibbonaci_iterate.exs

def fibbonaci_iterate do
  Stream.unfold([0, 1], fn [prev, curr] -> {curr, [curr, (prev + curr)]} end)
end

# fibbonaci_iterate |> Stream.take_every(10) |> Stream.map(fn(x) -> x * 2 end) |> Enum.take(5)
# [2, 178, 21892, 2692538, 331160282]
# note that the list was actually only enumerated once