Types can be read from the module’s bytecode like the following at compile-time:

defmodule MyModule do
  @type one_type :: atom()
  @opaque another_type :: integer()

  @after_compile {MyModule, :_collect_types}

  def _collect_types(_env, bytecode) do
    {:ok, types} = Code.Typespec.fetch_types(bytecode)

    Enum.map(types, fn {kind, type} ->
      type_ast = Code.Typespec.type_to_quoted(type)

      type_ast
      |> Macro.to_string()
      |> IO.inspect(label: kind)
    end)
  end
end

it prints:

opaque: "another_type() :: integer()"
type: "one_type() :: atom()"

You cannot. I have asked for such thing on the Erlang Issue Tracker and IRC and there is no way to achieve what you want. The only solution is to manually store 3rd element of the tuple returned by defmodule and use that as a BEAM data.

Good to know. It seems OTP has no public interface to get in-memory modules yet.