my_list.exs

defmodule MyList do
  def map([], _), do: []
  def map([head | tail], func), do: [func.(head) | map(tail, func)]

  def sum([], total), do: total
  def sum([head | tail], total), do: sum(tail, head + total)

  def mapsum([], _), do: 0
  def mapsum(list, func), do: sum(map(list, func), 0)
end