Persistent zipping (interleaving) in Elixir.

interleave.exs

defmodule Interleave do
  def interleave(a,     b,  result \\ [])
  def interleave([],    [], result), do: result |> Enum.reverse
  def interleave([],    b,  result), do: interleave(b, [], result)
  def interleave([h|t], b,  result), do: interleave(b, t, [h | result])
end

iex(1)> split = Regex.split(~r/x/, "fooxbar")
["foo", "bar"]
iex(2)> scan = Regex.scan(~r/x/, "fooxbar")
[["x"]]
iex(3)> Enum.zip(split, scan)
[{"foo", ["x"]}]
iex(4)> Interleave.interleave(split, scan)
["foo", ["x"], "bar"]