match_and_assign.exs

defmodule MatchAndAssign do
  defmacro __using__(_) do
    quote do
      require MatchAndAssign
      import MatchAndAssign, only: [match_and_assign: 2]
    end
  end

  defp unhygienize(pattern = {n, _meta, c}) when is_atom(n) and is_atom(c) do
    var! pattern
  end

  defp unhygienize({n, meta, l}) when is_atom(n) and is_list(l) do
    {n, meta, Enum.map(l, &unhygienize/1)}
  end

  defp unhygienize(tuple) when is_tuple(tuple) do
    tuple
    |> Tuple.to_list
    |> Enum.map(&unhygienize/1)
    |> List.to_tuple
  end

  defp unhygienize(list) when is_list(list) do
    Enum.map(list, &unhygienize/1)
  end

  defp unhygienize(other), do: other

  defmacro match_and_assign(val, pattern) do
    quote do
      unquote(unhygienize(pattern)) = unquote(val)
    end
  end
end


defmodule A do
  use MatchAndAssign

  def test do
    %{a: 1, b: 2}
    |> match_and_assign(y = %{a: x})
    IO.inspect x
    IO.inspect y
  end
end


A.test