(flet ((compute-new-rank (document)
         (loop for neighbor in (graph-neighbors document)
               sum (/ (* damping (rank neighbor) (document-similarity document neighbor))
                      (graph-neighbor-edge-sum neighbor)))))
  (loop named convergence
        for iteration from 0 to iteration-limit
        do (loop for document in documents
                 for old-rank = (rank document)
                 for new-rank = (compute-new-rank document)
                 do (setf (rank document) new-rank)
                 when (convergedp old-rank new-rank)
                   do (return-from convergence t))))