gistfile1.txt

λ iex my.ex 
Erlang/OTP 17 [erts-6.0] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]

Interactive Elixir (0.13.3-dev) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> use My
nil
iex(2)> 3&&4
81.0

my.ex

defmodule My do
  defmacro __using__(_) do
    quote do
      # import all macros from My
      import unquote(__MODULE__)

      # hide macros from Kernel
      import Kernel, except: [&&: 2]
    end
  end

  defmacro left && right do
    :math.pow(left, right)
  end
end