delete_all.ex

defmodule MyList  
  def delete_all(list, el) do 
    _delete_all(list, el, [])
    |> Enum.reverse()
  end

  def _delete_all([el | tail], el, new_list) do
    _delete_all(tail, el, new_list)
  end

  def _delete_all([head | tail], el, new_list) do 
    _delete_all(tail, el, [head | new_list])
  end

  def _delete_all([], el, new_list) do 
    new_list
  end  
end