input: Write a python function to calculate the sum of elements in a list recursively.
  assert sumOfList([1, 2, 3, 4, 5]) == 15
  assert sumOfList([10, -2, 3, 7]) == 18
  assert sumOfList([5]) == 5
output: def sumOfList(lst):
      if not lst:
          return 0
      else:
          return lst[0] + sumOfList(lst[1:])