common-lisp Recursion Compute nth Fibonacci number
Example
;;Find the nth Fibonacci number for any n > 0.
;; Precondition: n > 0, n is an integer. Behavior undefined otherwise.
(defun fibonacci (n)
(cond
( ;; Base case.
;; The first two Fibonacci numbers (indices 1 and 2) are 1 by definition.
(<= n 2) ;; If n <= 2
1 ;; then return 1.
)
(t ;; else
(+ ;; return the sum of
;; the results of calling
(fibonacci (- n 1)) ;; fibonacci(n-1) and
(fibonacci (- n 2)) ;; fibonacci(n-2).
;; This is the recursive case.
)
)
)
)
