Replace `^variable` with the variable value with Elixir macro

replace_macro.ex

defmodule Foo do
  defmacro select(columns) when is_list(columns) do
    # in macro context we replace all `^foo` forms with `foo`
    columns = Macro.postwalk(columns, &interpolate/1)

    IO.inspect(columns, label: :columns_after_interpolate)

    # we unquote in the caller context, and map atoms to Columns after all
    # `^foo` were replaced with `foo`
    quote do
      Enum.map(unquote(columns), &Foo.atom_to_column/1)
    end
  end

  def interpolate({:^, _, [{name, _ctx, _env} = v]}) when is_atom(name) do
    IO.inspect(v, label: :replaced_in_function)
    v 
  end
  def interpolate(x), do: x

  # column conversion logic

  defmodule Column do
    defstruct [:name]
  end

  def atom_to_column(a) when is_atom(a) do
    %Column{name: a}
  end

  def atom_to_column(a), do: a
end

import Foo
c = select([:foo, :bar])

bar = :foobar
c = select([:foo, ^bar])