(defun get-longest-path (nodes node-id visited) (declare (optimize (speed 3) (space 0) (debug 0) (safety 0) (compilation-speed 0)

(defun get-longest-path (nodes node-id visited) (declare (optimize (speed 3) (space 0) (debug 0) (safety 0) (compilation-speed 0) #+lispworks (fixnum-safety 0)) (type fixnum node-id) (type (vector node) nodes) (type (vector atom) visited)) (setf (aref visited node-id) t) (Let ((max (loop for neighbour of-type route across (node-neighbours (aref nodes node-id)) unless (aref visited (route-dest neighbour)) maximize (the fixnum (+ (the fixnum (route-cost neighbour)) (the fixnum (get-longest-path nodes (route-dest neighbour) visited))))))) (declare (fixnum max)) (setf (aref visited node-id) nil) max)) Above Common Lisp version improves the runtime from 8.5 to 3.6 seconds in SBCL and from 30 seconds to 2 seconds in LispWorks 64bit. Computer: i7 Mac mini.