From the little elixir and OTP book. This exercise is about using `Stream` to do some lazy enumeration. The takeaway is that the _last_ enumerable thing has to be an enumerable.

stream_lines.ex

defmodule StreamLines do

  @path "./some_text.txt"
  def large_lines!(path \\ @path) do
    path
    |> File.stream!
    |> Stream.map(&String.replace(&1, "\n", ""))
    |> Enum.filter(&(String.length(&1) > 70))
  end

  def lines_lengths!(path \\ @path) do
    path
    |> File.stream!
    |> Enum.map(&String.length(&1))
  end

  def longest_line_length!(path \\ @path) do
    path
    |> File.stream!
    |> Stream.map(&String.length(&1))
    |> Enum.sort(&(&1 > &2))
    |> hd
  end

  def longest_line!(path \\ @path) do
    path
    |> File.stream!
    |> Stream.with_index
    |> Stream.map(&({elem(&1, 0), String.length(elem(&1, 0)), elem(&1, 1)}))
    |> Enum.sort(&(elem(&1, 1) > elem(&2, 1)))
    |> hd
    |> elem(0)
  end

  def words_per_line!(path \\ @path) do
    path
    |> File.stream!
    |> Stream.map(&String.split(&1))
    |> Enum.map(&(Enum.count(&1)))
  end
end