Euler2.exs

# sum of fibonacci numbers which is even and less than 4000000 

# https://elixirforum.com/t/project-euler-problem-2/500/2

defmodule Problem2 do

  def fib_seq do
    Stream.unfold({1,1}, fn {a,b} -> {a, {b, a + b}} end)
  end
  
  def solve(limit) do
    fib_seq
    |> Stream.take_while(&(&1 < limit))
    |> Stream.filter(&(rem(&1, 2) == 0))
    |> Enum.sum
  end

  def print do
    IO.puts solve(4000000)
  end

end

Problem2.print