Mrs Senora Ada Nev, a descendant of the (in)famous Ada Lovelace and an AP/CS teacher in the wild, wild west, has finally understood trees. Here is her data definition:

(define-struct two (left center right))
(define-struct thr (left up down right))

;; A 2-3-Tree is one of: 
;; -- a Number 
;; -- (make-two 2-3-Tree Number 2-3-Tree)
;; -- (make-thr 2-3-Tree Number Number 2-3-Tree)

Now she wants you to create a template for functions that process 2-3-Trees:

;; ff : 2-3-Tree -> ???
;; to do something with a 2-3-Tree

Solution:

Grader: Richard

;; [PTS: 5
;;  -- 1 for 3 correct cond clauses
;;  -- 2 4/5 correctly used selectors
;;  -- 2 for 4 correct natural recursions]
(define (ff t23)
  (cond
    [(number? t23) ...]
    [(two? t23) 
     ... (ff (two-left t23)) ... 
     ... (two-center t23) ...
     ... (ff (two-right t23))]
    [(thr? t23) 
     ... (ff (thr-left t23)) ...
     ... (thr-up t23) ...
     ... (thr-up t23) ...
     ... (ff (thr-right t23))]))