test.exs

defmodule Test do
  def sum(list), do: _sum(list, 0)

  defp _sum([], acc),     do: acc
  defp _sum([x|xs], acc), do: _sum(xs, acc+x)

  def max(list), do: _max(list, Enum.first(list))

  defp _max([], max),     do: max
  defp _max([x|xs], max)
    when x > max,         do: _max(xs, x)
  defp _max([x|xs], max), do: _max(xs, max)
end

test.hs

sum list = sum' list 0
  where sum' [] acc = acc
        sum' (x:xs) acc = sum' xs acc+x

max list = max' list (head list)
  where max' [] max = max
        max' (x:xs) max
          | x > max   = max' xs x
          | otherwise = max' xs max