;; The first three lines of this file were inserted by DrScheme. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname recursive_structures) (read-case-sensitive #t) (teachpacks ((lib "testing.ss" "teachpack" "htdp") (lib "guess.ss" "teachpack" "htdp") (lib "master.ss" "teachpack" "htdp") (lib "draw.ss" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "testing.ss" "teachpack" "htdp") (lib "guess.ss" "teachpack" "htdp") (lib "master.ss" "teachpack" "htdp") (lib "draw.ss" "teachpack" "htdp")))))
;; the book example Ch. 14

;; a child structure represents a person
;; father and mother are "child" structures that 
;; represent the person's parents
;; or empty if there is no data on a parent
;; name is a symbol (the person's name)
;; date is a positive integer (year of birth)
;; eyes is a symbol that represents the color of the eyes
(define-struct child (father mother name date eyes))

;; Oldest Generation:
(define Carl (make-child empty empty 'Carl 1926 'green))
(define Bettina (make-child empty empty 'Bettina 1926 'green))

;; Middle Generation:
(define Adam (make-child Carl Bettina 'Adam 1950 'yellow))
(define Dave (make-child Carl Bettina 'Dave 1955 'black))
(define Eva (make-child Carl Bettina 'Eva 1965 'blue))
(define Fred (make-child empty empty 'Fred 1966 'pink))

;; Youngest Generation: 
(define Gustav (make-child Fred Eva 'Gustav 1988 'brown))

;; blue-eyed-ancestor? : ftn  ->  boolean
;; to determine whether a-ftree contains a child
;; structure with 'blue in the eyes field
(define (blue-eyed-ancestor? a-ftree)
  (cond
    [(empty? a-ftree) false] ;; base case
    [else (cond
            [(symbol=? (child-eyes a-ftree) 'blue) true] ;; another base case
            ;; recursive call, father node:
            [(blue-eyed-ancestor? (child-father a-ftree)) true] 
            ;; recursive call, mother node:
            [(blue-eyed-ancestor? (child-mother a-ftree)) true]
            [else false])]))

(blue-eyed-ancestor? Carl)
;; expected
false

(blue-eyed-ancestor? Gustav)
;; expected 
true

;; count-persons: family tree node -> integer
;; consumes a family tree node
;; counts how many people are there in the known family tree
;; rooted in the node
(define (count-persons a-tree) 
  (cond
    [(empty? a-tree) 0]
    [else (+ 1 (count-persons (child-father a-tree)) (count-persons (child-mother a-tree)))]
  )
)

(count-persons Adam)
;; expected 
3

(count-persons Gustav)
;; expected
5


;; eye-colors: family tree node -> list of symbols
;; consumes a family tree node and produces a list of all eye colors 
;; in the tree. An eye color may occur more than once in the list.
(define (eye-colors a-tree)
  (cond
    [(empty? a-tree) empty]
    [else (cons (child-eyes a-tree)
                (append 
                 (eye-colors (child-father a-tree)) 
                 (eye-colors (child-mother a-tree))))]
  )
)


(eye-colors Adam)
;; expected 
(list 'yellow 'green 'green)

(eye-colors Gustav)
;; expected 
(list 'brown 'blue 'green 'green 'pink)