gistfile1.ex

defmodule Challenge do
  def printer("", acc) do
    acc
  end
  
  def printer("%%d" <> rest, acc) do
    fn int ->
      next = acc <> to_string(int)
      printer(rest, next)
    end
  end

  def printer("%%s" <> rest, acc) do
    fn str ->
        printer(rest, acc <> str)
    end
  end

  def printer(expr, acc) do
    [h| t] = String.codepoints(expr)
    printer(to_string(t), acc <> h)
  end

  def printf(str) do
    printer(str, "")
  end
end

Challenge.printf("hello %%d %%s").(1).("world") |> IO.puts