# 040: Tail Recursion
# Efficient recursion (last call is recursive call)

# Regular recursion (not tail-recursive)
factorial_regular(n):
  if n <= 1:
    return 1
  return n * factorial_regular(n - 1)  # Multiplication happens AFTER recursive call

# Tail-recursive version (with accumulator)
factorial_tail(n, accumulator = 1):
  if n <= 1:
    return accumulator
  return factorial_tail(n - 1, n * accumulator)  # Recursive call is LAST thing

show factorial_tail(5)  # 120

# Sum with tail recursion
sum_tail(numbers, accumulator = 0):
  if numbers.length == 0:
    return accumulator
  return sum_tail(numbers[1:], accumulator + numbers[0])

show sum_tail([1, 2, 3, 4, 5])  # 15

# Range generator
make_range(start, end, result = []):
  if start > end:
    return result
  result.append(start)
  return make_range(start + 1, end, result)

show make_range(1, 10)  # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]