epai

  1.  def fib(n):
  2.      i, curr, next = 0, 0, 1
  3.      while i < n:
  4.          i += 1
  5.          curr, next = next, curr + next
  6.      return curr

  1.  def fib(n):
  2.      def fib_tail(i, curr, next):                  #1
  3.          if i >= n:                                #2
  4.              return curr                           #3
  5.          return fib_tail(i+1, next, curr+next)     #4
  6.      return fib_tail(0, 0, 1)