tree_seq.rkt

#lang racket
(require srfi/1)

(define (walk-bfs-n node)
  ;; ((walk-bfs-n '(a (b c d) e)) list)
  (lambda (k)
    (if (list? node)
        (let* ((label (first node))
               (nodes (rest node))
               (labels (map (lambda (node) (call/cc (walk-bfs-n node))) nodes)))
          (append labels (k label)))
        (k node))))

(define (walk-dfs-n node)
  ;; (call/cc (walk-dfs-n '(a (b c d) e)))
  (lambda (k)
    (if (list? node)
        (let* ((label (car node))
               (nodes (cdr node))
               (seqs (map (lambda (node) (call/cc (walk-dfs-n node))) nodes)))
          (k (apply append (list label) seqs)))
        (k (list node)))))

(define (tree->seq node i)
  ;; i is a index 
  (if (list? node)
      (let* ((label (car node))
             (children (cdr node))
             (recur (lambda (elm acc)
                      (let ((j (+ (car (last (last acc))) 1)))
                        (append acc (list (tree->seq elm j))))))
             (initial (list (tree->seq (car children) (+ i 1))))
             (seqs (foldl recur initial (cdr children)))
             (tags (map caar seqs)))
        (cons (cons* i label tags) (apply append seqs)))
      (list (list i node))))