Python tests

def f(arr):
    return arr[0] if len(arr) == 1 else arr[0] + f(arr[1:])
print(f([]))

def f(a: int = 2, b: int = 2) -> int:
    return a ** b
print(f(3))

def f(arr):
    return 0 if not arr else arr[0] + f(arr[1:])
print(f(('a', 'b', 'c', 'd')))