facade.ex

defmodule MyApp.Facade do

  defmacro facade(mod) do
    quote bind_quoted: [mod: mod] do
      Enum.each apply(mod, :__info__, [:functions]), fn {fun, arity} ->
        case arity do
          0 -> defdelegate unquote(fun)(), to: mod
          _ ->
            values = Enum.map(1..arity, &(Macro.var(:"arg#{&1}", mod)))
            defdelegate unquote(fun)(unquote_splicing(values)), to: mod
        end
      end
    end
  end

end

my_app.ex

defmodule MyApp.Blog do
  import MyApp.Facade

  facade MyApp.Blog.PostContext
  facade MyApp.Blog.CommentContext
end

# MyApp.Blog.create_post/1 -> MyApp.Blog.PostContext.create_post/1
# MyApp.Blog.create_comment/2 -> MyApp.Blog.CommentContext.create_comment/2

Fixed issue with 0-arity functions