RosettaCodeData/Task/Fibonacci-sequence/Fe/fibonacci-sequence-2.fe

(= fib (fn (n)
  (let p0 0)
  (let p1 1)
  (while (< 0 n)
    (= n (- n 1))
    (let tmp (+ p0 p1))
    (= p0 p1)
    (= p1 tmp))
  p0))