Function: TREE-BEAM-SEARCH

Source

(defun tree-beam-search (start goal-p successors cost-fn beam-width)
  (tree-search (list start) goal-p successors
	       (lambda (old new)
		 (let ((sorted (funcall (sorter cost-fn) old new)))
		   (if (> beam-width (length sorted))
		       sorted
		       (subseq sorted 0 beam-width))))))