Solution to StringsAndBinaries-4 (Programming Elixir)

my_string.ex

defmodule MyString do
  def calculate(to_calc) do
    {f, op, s} = _calculate(to_calc)
    apply(Kernel, op, [f, s])
  end

  def _calculate(t, acc \\ []) # Default value for acc
  def _calculate([ ?\s | t ], acc), do: _calculate(t, acc) # Scape spaces
  def _calculate([h|t], acc) when h in [?+, ?-, ?/, ?*] do
    {to_digit(acc), List.to_atom([h]), to_digit(_calculate(t))}
  end
  def _calculate([h|t], acc), do: _calculate(t, acc ++ [h])
  def _calculate([], acc), do: acc

  defp to_digit(acc), do: String.to_integer(List.to_string(acc))
end