;; update-year:  ftnode string number -> ftnode
;; consumes a family tree, a name and a new year and produces a tree the same as the original
;;except that the named person has the given year
(define (update-year aft name year)
  (cond [(symbol? aft) 'unknown]
        [(person? aft)  (cond [(string=? name (person-name aft))
                               (make-person name
                                            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" 1962) 
              (make-person "Mary" 1980 'blue
               (make-person "Ann" 1962 'green
                            'unknown
                            (make-person "Fred" 1936 'blue
                                         'unknown
                                         'unknown))
               (make-person "Joe" 1960 'blue
                            'unknown
                            'unknown)))
(check-expect (update-year 'unknown "Ann" 1962) 'unknown)