visit.clj

visit.clj

(defn visit [m visitors]
  ;; [node node-s next-s down-s right-s get-right get-down init-right-s cut-down cut-right :as m]
  ;; {:keys [break]} next-s
  ;; ;use next-state by default, unless down or right is necessary
  (let
    [dovisit (fn [m dir]
               (loop [s m [v & vs] visitors]
                 (if v (recur (apply v (concat [dir] s)) vs) s)))
     m2 (dovisit m :pre)
     ;break/cut checks should be between each visitor (:pre :post and :in) according to zip-visit
     ;https://github.com/akhudek/zip-visit/blob/master/src/zip/visit.cljc#L5
     ;(if (or b c)
     ;     {:node node* :state state* :break b :cut c}
     m3
     (let [[node* _ next-s* _ _ _ get-down* init-right-s* cut-down _] m2]
       (if-let [down* (and (not cut-down)
                           (not (:break next-s*))
                           (get-down* node*))]
         (assoc m2 2 (nth
                       (visit
                         (assoc m2
                                0 down*
                                1 nil
                                4 init-right-s*)
                         visitors) 2)
                   8 false)
         (assoc m2 8 false)))
     m4 (dovisit m3 :mid)
     m5
     (let [[_ _ _ down-s _ _ _ _ _ _] m
           [node* _ next-s* _ _ get-right* _ _ _ cut-right] m3]
       (if-let [right* (and (not cut-right)
                            (not (:break next-s*))
                            (get-right* node*))]
                (let [mm
                       (visit
                         (assoc m4
                                0 right*
                                1 nil
                                3 down-s)
                         visitors)]
         (assoc m4 2 (nth mm 2)
                   9 false))
         (assoc m4 9 false)))
    m6 (dovisit m5 :post)]
    m6
    ;:in (needs get-up, such that an :in visitor can't replace the node), :in happens after post, it's about operations in the context of the parent between each child
    ))

;; probably can be made either non-recursive or loop/recur using zippers