;; A ftnode is either
;;   - 'unknown or
;;   - (make-person string number symbol ftnode ftnode)
(define-struct person (name year eye mother father))

;; Example

(define MaryTree
  (make-person "Mary" 1980 'blue
               (make-person "Ann" 1960 'green
                            'unknown
                            (make-person "Fred" 1936 'blue
                                         'unknown
                                         'unknown))
               (make-person "Joe" 1960 'blue
                            'unknown
                            'unknown)))

;; update-year:  ftnode string number -> ftnode
;; consumes a family tree node, a name, and a birth year.  The function
;; produces a ftnode the same as the original except that the birth year
;; of the named person is now the given birth year
(define (update-year aft name year)
  (cond [(symbol? aft) aft]
        [(person? aft)
         (cond [(string=? (person-name aft) name)
                (make-person (person-name aft)
                             year
                             (person-eye aft)
                             (person-mother aft)
                             (person-father aft))]
               [else
                (make-person (person-name aft)
                             (person-year aft)
                             (person-eye aft)
                             (update-year (person-mother aft) name year)
                             (update-year (person-father aft) name year))])]))



;; test
(check-expect (update-year MaryTree "Ann" 1958)
              (make-person "Mary" 1980 'blue
                           (make-person "Ann" 1958 'green
                                        'unknown
                                        (make-person "Fred" 1936 'blue
                                                     'unknown
                                                     'unknown))
                           (make-person "Joe" 1960 'blue
                                        'unknown
                                        'unknown)))

(check-expect (update-year MaryTree "Bruce" 1939) MaryTree)
(check-expect (update-year 'unknown "Sally" 1965) 'unknown)

;; gather-blue-eyed:  ftnode -> list-of-string
;; consumes a family tree node and produces a list of the names of all
;; people in the tree who have blue eyes
(define (gather-blue-eyed aft)
  (cond [(symbol? aft) empty]
        [(person? aft)
         (cond [(symbol=? 'blue (person-eye aft))
                (append
                 (list (person-name aft))                 
                 (gather-blue-eyed (person-mother aft))    
                 (gather-blue-eyed (person-father aft)))]
               [else (append (gather-blue-eyed (person-mother aft))
                             (gather-blue-eyed (person-father aft)))])]))

;; test
(check-expect (gather-blue-eyed 'unknown) empty)
(check-expect (gather-blue-eyed MaryTree) (list "Mary" "Fred" "Joe"))