;; represent a family tree, where each person in the tree has a name,
;; year of birth, eye color, mother, and father

(define-struct person (name year eye mother father))
;; a Person is a (make-person String Natural String Treenode Treenode)
;; interp:  a person in a family tree where
;;    name
;;    year
;;    eye
;;    mother, father are the roots of the person's mother's and father's trees


;; a Treenode is one of
;;    false
;;    Person
;;  interp:  Treenode represents a family tree

(define MARYTREE
  (make-person "Mary" 1980 "blue"
               (make-person "Ann" 1960 "green"
                            false
                            (make-person "Fred" 1936 "blue"
                                         false
                                         false))
               (make-person "Joe" 1960 "blue"
                            false
                            false)))

;;; treenode-fcn:  Treenode ->
;;;
;(define (treenode-fcn atn)
;  (cond [(boolean? atn) (...)]
;        [(person? atn) (... (person-name atn)
;                            (person-year atn)
;                            (person-eye atn)
;                            (treenode-fcn (person-mother atn))
;                            (treenode-fcn (person-father atn)))]))


;; count-blue-eyed:  Treenode -> Natural
;; consumes a family tree and produces the number of people in the tree with blue eyes
(define (count-blue-eyed atn)
  (cond [(boolean? atn) 0]
        [(person? atn) (if (string=? (person-eye atn) "blue")
                           
                           (+ 1 
                              (count-blue-eyed (person-mother atn))
                              (count-blue-eyed (person-father atn)))
                           
                           (+ (count-blue-eyed (person-mother atn))
                              (count-blue-eyed (person-father atn))))]))


(check-expect (count-blue-eyed false) 0)
(check-expect (count-blue-eyed MARYTREE) 3)