AEM multiplication

AEM_Step5.exs

 defmodule AncientEgyptianMultiplication do
  require Integer
   def multiply(first, second) do
      decomposed = decompose(first)
      multiply(decomposed, second, [])
    end

    def multiply([], _, state), do: sum_of(state)
    # 128 × 13 + 64 × 13 + 32 × 13 + 8 × 13 + 4 × 13 + 2 × 13
    def multiply([head | tail], second, state) do
      state = state ++ [head * second]
      multiply(tail, second, state)
    end
  end