Allow collecting into an integer for sums in elixir

ext-integer.ex

defmodule ExtInteger do
  defimpl Collectable, for: Integer do
    @doc """
    Collect into: an integer
    
    ## Examples
    
        iex> for n <- 1..5, into: 0, do: n
        15
    """
  
    def into(num) do
      fun = fn
        acc, {:cont, n} -> acc + n
        acc, :done -> acc
        _, :halt -> :ok
      end

      {num, fun}
    end
  end
end