Function: FOLLOW-ARC

Source

(defun follow-arc (component extend? trie)
  (let ((arc (assoc component (trie-arcs trie))))
    (cond ((not (null arc)) (cdr arc))
	  ((not extend?) nil)
	  (t (let ((new-trie (make-trie)))
	       (push (cons component new-trie)
		     (trie-arcs trie))
	       new-trie)))))