graph.clj

(letfn [(incoming-exists? [id exists?]  (and exists? (not (node-deleted? id))))
        (edge-deleted?    [id deleted?] (or deleted? (node-deleted? id)))
        (edge-deleted     [id edge]     (update edge :deleted (partial edge-deleted? id)))]
  (defn- mark-edges-deleted [keyseq node incoming]
    (cond-let [ks (edges-keyseq keyseq)]
              (update-in node ks map-vals-with-keys
                         (if incoming?
                           incoming-exists?
                           edge-deleted))
              [ks (deleted-edge-keyseq keyseq)]
              (update-in node ks
                         (if incoming?
                           incoming-exists?
                           edge-deleted?))
              :else node)))