macros.ex

defmodule Scope do
  defmacro update_local(val) do
    local_var = "first"
    result = quote do
      local_var = unquote(val)
      IO.puts "In macro usage: #{local_var}"
    end
    IO.puts "In macro definition: #{local_var}"
    result
  end
end

defmodule Test do
  require Scope

  local_var = "third"
  Scope.update_local("second")
  IO.puts "On return: #{local_var}"
end