;; 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-intermediate-reader.ss" "lang")((modname nested_lists) (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")))))
;; lists of lists

(define lists (list 1 2 (list 4 5) (list 3 (list 6))))

;; sum-nested-lists: list of lists of numbers -> integer
;; the function takes a list of lists of numbers of
;; arbitrary nesting and finds the sum of all its elements
;; (sum-nested-lists (list 1 2 (list 4 5) (list 3 (list 6)))
;; -> 21
;; we assume that lol is a valid list of numbers
(define (sum-nested-lists lol) 
  (cond 
    [(empty? lol) 0]
    [(number? (first lol)) (+ (first lol) (sum-nested-lists (rest lol)))]
    [else (+ (sum-nested-lists (first lol)) 
                            (sum-nested-lists (rest lol)))]
  )
)

(sum-nested-lists (list 1 2 (list 4 5) (list 3 
                                             (list 6))))
;; expected value
21

(sum-nested-lists (list 1 2 (list 4 5) 3 6))
;; expected value
21

(sum-nested-lists empty)
;; expected value 
0

;; contains?: number, list of lists of numbers -> boolean
;; the function takes a number and a list of lists of numbers 
;; of arbitrary nesting and returns true if the given number 
;; appears in the list and false otherwise
(define (contains? lol num)
  (cond
    [(empty? lol) false]
    [(and (number? (first lol)) (= (first lol) num))
     true]
    ;; a number not equal to num:
    [(number? (first lol)) (contains? (rest lol) num)]
    [else (or (contains? (first lol) num)
              (contains? (rest lol) num))]
   )
)

(contains? (list 2 (list 4 5) (list 7 8)) 3)
;; expected
false

(contains? (list 2 (list 4 5) (list 7 3)) 3)
;; expected
true

(contains? (list 2 (list 3 5) (list 7 3)) 3)
;; expected
true

(contains? (list 2 (list 2 (list 2 (list 3)))) 3)
;; expected
true

(contains? (list 2 (list 2 (list 2 (list 4)))) 3)
;; expected
false