zip_blog_post_2.ex

defprotocol Zip do
  def apply(collection_1, collection_2, operation)
end

# We can implement it for lists:
defimpl Zip, for: List do
  def apply(a, b, calculate) do
    Enum.zip(a, b)
    |> Enum.map(fn {a, b} -> calculate.(a, b) end)
  end
end

# Now our zip works:
Zip.apply([1, 2], [3, 4], fn x, y -> x + y end) #=> [4, 6]