;; Functions to calculate Fibonacci numbers

;; Slow recursive version
(def slowFib (fn (n) (if (< n 2) n (+ (slowFib (- n 1)) (slowFib (- n 2))))))

;; Return the sum of the last 2 numbers in a sequence
(def sumOfLast (fn (l) (+ (last l) (penult l))))

;; Faster version, return vector of n numbers, tail call optimized
(def fibListRec (fn (n l) (if (< (len l) n) (fibListRec n (push l (sumOfLast l))) l)))
(def fibList (fn (n) (fibListRec n [0 1])))
(def fastFib (fn (n) (sumOfLast (fibList n))))