Fun with Elixir macros and Streams

timing.exs

defmodule Timing do
  def now do
    :os.system_time(:milli_seconds)
  end

  # broken! the block is executed immediately
  #
  def ftime([do: block]) do
    t0 = now
    { :ok, block, now - t0 }
  end

  # ok. The block is "placed" where it is unquoted,
  # and executed later
  #
  defmacro mtime([do: block]) do
    quote do
      t0 = Timing.now
      { :ok, unquote(block), Timing.now - t0 }
    end
  end
end

# ---------------------------
# Enum vs Stream


require Timing


{ :ok, result, ms } = Timing.mtime do
  Enum.map(1..10_000_000, &(&1+1)) |> Enum.take(5)
end
# {:ok, [2, 3, 4, 5, 6], 14157}


{ :ok, result, ms } = Timing.mtime do
  Stream.map(1..10_000_000, &(&1+1)) |> Enum.take(5)
end
# {:ok, [2, 3, 4, 5, 6], 1}


# Broken function implementation
{ :ok, result, ms } = Timing.ftime do
  Enum.map(1..10_000_000, &(&1+1)) |> Enum.take(5)
end
# {:ok, [2, 3, 4, 5, 6], 0}