;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-advanced-reader.ss" "lang")((modname week4_tu_full) (read-case-sensitive #t) (teachpacks ((lib "image.ss" "teachpack" "2htdp"))) (htdp-settings #(#t constructor repeating-decimal #t #t none #f ((lib "image.ss" "teachpack" "2htdp")))))
; a list-of-numbers is:
;   empty, or
;   (cons number list-of-numbers)
; template:
; (define (fun-for-list-of-numbers numlist)
; (cond [(empty? numlist) ...]
;       [(cons? numlist) ... (first numlist) ... (fun-for-list-of-numbers (rest numlist)) ... ])

; Q1: write the following function:
; double-list: list-of-numbers -> list-of-numbers
; inserts a duplicate of each list element x immediately following x
(define (double-list numlist)
 (cond [(empty? numlist) empty]
      [(cons? numlist) (append (list (first numlist) (first numlist)) 
                               (double-list (rest numlist)))])
  )


(check-expect (double-list (list 1 2 3)) (list 1 1 2 2 3 3))
(check-expect (double-list empty) empty)
(check-expect (double-list (list 1 1)) (list 1 1 1 1))

; A ftn is either
  ; - empty
  ; - (make-child name date eyes mom dad)
; where a child is
; - symbol name
; - number date (a year)
; - symbol eyes (a color)
; - ftn mom
; - ftn dad
(define-struct child (name date eyes mom dad))

; template:
; (define (fun-for-ftn a-ftree)
;  (cond
;    [(empty? a-ftree) ...]
;    [else
;      ... (child-name a-ftree) ...
;      ... (child-date a-ftree) ...
;      ... (child-eyes a-ftree) ...
;      ... (fun-for-ftn (child-dad a-ftree)) ...
;      ... (fun-for-ftn (child-mom a-ftree)) ...
;]))

; examples:
;; Grandparents
(define Dave (make-child 'Dave 1937 'black empty empty))
(define Eva (make-child 'Eva 1934 'blue empty empty))
(define Fred (make-child 'Fred 1930 'pink empty empty))
(define Greta (make-child 'Greta 1933 'brown empty empty))

;; Parents
(define Carl (make-child 'Carl 1967 'green Eva Dave))
(define Bettina (make-child 'Bettina 1966 'green Greta Fred))

;; Youngest Generation: 
(define Adam (make-child 'Adam 1990 'yellow Bettina Carl))

; Q2 write the following function:
; tree-size ftn -> number
; returns the total number of people in a tree
(define (tree-size a-ftree) 
  (cond [(empty? a-ftree) 0]
        [else (+ 1 (tree-size (child-mom a-ftree)) (tree-size (child-dad a-ftree)))]))
(check-expect (tree-size Dave) 1)
(check-expect (tree-size Adam) 7)

;; Q3 write the following function:
; forget-history: ftn number -> ftn
; returns the same family tree but with all ancestors before given year removed
(define (forget-history a-ftree year) 
  (cond [(empty? a-ftree) empty]
        [else 
         (cond [(< (child-date a-ftree) year) empty]
               [else
                          (make-child (child-name a-ftree)
                          (child-date a-ftree)
                          (child-eyes a-ftree) 
                          (forget-history (child-mom a-ftree) year)
                          (forget-history (child-dad a-ftree) year))])]))

(check-expect (forget-history Adam 1989) (make-child 'Adam 1990 'yellow empty empty))
(check-expect (forget-history Adam 1900) Adam)