A simple recursion example using pattern matching.

math.ex

defmodule Math do
  def sum_list([number]) do
    number
  end
  
  def sum_list([head|tail]) do
    head + sum_list(tail)
  end
end

# Examples:
#   Math.sum_list([10])
#   # => 10
#
#   Math.sum_list([17, 13, 7, 5])
#   # => 42