See my last paragraph here: I don't understand quote/unquote: why do we need them?

More on unquote fragments: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#quote/2-binding-and-unquote-fragments

You could build the macro to be called like that:

content(conn) do
  IO.inspect(conn)
end

or

content conn do
 IO.inspect(conn)
end

I’d not jump to unhygienic variables without a good reason.

I personally prefer something like:

content do
  conn -> IO.inspect(conn)
end

You can either decompose it to grab the head as the var, or just use it as a case context with full matching and all, which is also so easy to do in quotes.

Using var! makes the variable unhygienic, so it bleeds into the inner blocks scope. If you consider the resulting AST you’ll notice, that the inner block just refers to a variable like this {:conn, [], Some.Module}, where the last part is the context of the variable. var! makes it so that the contexts match, while without that they won’t.

The resulting AST doesn’t really care if it came out of a macro or not. With it it looks like you wrote:

      def page_view(conn) do
        import Kernel, except: [div: 2, to_string: 1]
        import ExAdmin.ViewHelpers
        use Xain
        _ = conn

        markup safe: true do
          IO.inspect(conn)
        end
      end

Which is obviously fine code.

I like very much your idea. Can you give an example how can I write a macro like this?
I would like to be able to call it like this:

wrap_with_connection do
   channel -> publish_on_existing_channel(channel, @exchange, @outcome_routing_key, outcome_payload)
end

I can not figure out how to write the macro. What I have by now is:

defmodule Example do
  def init_rabbitmq_channel do
    ...
  end

  def close_rabbitmq_channel(channel) do
    ....
  end

  def publish_on_existing_channel(channel, exchange, routing_key, payload) do
    .....
  end

  defmacro wrap_with_connection(do: block) do
    quote do
      var!(channel) = init_rabbitmq_channel()
      unquote(block)
      close_rabbitmq_channel(channel)
    end
  end
end