hygienic macro support

[slepher]

-module(macro_example).
macro_with_vars_1(Ast) ->
    quote(
      begin
          A = 10,
          B = unquote(Ast),
          A + B
      end
     ).
macro_with_vars_2(Ast) ->
    quote(
      begin
          A = 10,
          B = unquote(Ast),
          A + B
      end
     ).

test_macro_with_vars(N) ->
    A1 = macro_with_vars_1(N),
    A2 = macro_with_vars_2(A1),
    A3 = macro_with_vars_2(N),
    A4 = macro_with_vars_1(A1),
    A1 + A2.

=>

test_macro_with_vars(N) ->
A1 =
begin
  A@macro_example@_1 = 10,
  B@macro_example@_1 = N,
  A@macro_example@_1 + B@macro_example@_1
end,
A2 = 
begin
  A@macro_example@_3 = 10,
  B@macro_example@_3 = A1,
  A@macro_example@_3 + B@macro_example@_3
end,
A3 = 
begin
  A@macro_example@_4 = 10,
  B@macro_example@_4 = N,
  A@macro_example@_4 + B@macro_example@_4
end
A4 =
begin
  A@macro_example@_2 = 10,
  B@macro_example@_2 = A1,
  A@macro_example@_2 + B@macro_example@_2
end
A1 + A2 + A3 + A4.

[slepher]

How elixir impl in macro.ex

# Expand possible macro require invocation
  defp do_expand_once({{:., _, [left, right]}, meta, args} = original, env) when is_atom(right) do
    {receiver, _} = do_expand_once(left, env)

    case is_atom(receiver) do
      false ->
        {original, false}

      true ->
        expand = :elixir_dispatch.expand_require(meta, receiver, {right, length(args)}, args, env)

        case expand do
          {:ok, receiver, quoted} ->
            next = :elixir_module.next_counter(env.module)
            {:elixir_quote.linify_with_context_counter(0, {receiver, next}, quoted), true}

          :error ->
            {original, false}
        end
    end
  end

[slepher]

done.