Elixir : Measure the execution time of an 'exp'

timer.ex

defmodule Timer do
  @moduledoc """
  Helper module to measure the execution time of an 'exp'
  """

  @doc """
  Measure the execution time of 'exp'.

  ## Parameters

    - unit: :second | :millisecond | :microsecond | :nanosecond | :native
  """
  defmacro duration(unit, do: exp) do
    quote do
      t1 = :os.system_time unquote(unit)
      unquote(exp)
      t2 = :os.system_time unquote(unit)
      t2 - t1
    end
  end
end

Also, using the :timer module

{us, :ok} = :timer.tc(IO, :puts, ["Hello World"])
# us : in microseconds (divide by 1_000_000 to get seconds)

:timer.tc(IO, :puts, ["Hello World"])
# {22, :ok}

add = fn (x, y) ->  x + y end
:timer.tc(add, [1,3])
# {5, 4}

:timer.tc(fn -> 
    # ...
    :ok
  end)
# {1_302_342, :ok}