friedman_ackermann.lisp

(in-package :cl-user)

(ql:quickload :optima)

(defpackage :ack-mann
  (:use :common-lisp :optima)
  (:export :ackermann))

(in-package :ack-mann)

(defun ackermann (s n)
  (if (not (consp s))
      n
      (let ((k (car s))
	    (r (rest s)))
	(match (cons k n)
	  ((cons 1 _) (ackermann r (* 2 n)))
	  ((cons _ 1) (ackermann (cons (1- k) r) 1))
	  ((cons _ _) (ackermann (cons k (cons (1- k) r))
				 (1- n))))))) 

; (ackermann '(3) 5)