;; 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-beginner-reader.ss" "lang")((modname lists) (read-case-sensitive #t) (teachpacks ((lib "universe.ss" "teachpack" "2htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "universe.ss" "teachpack" "2htdp")))))
(define L1 (cons 42 (cons 69 (cons 613 empty))))

(first L1)
(rest L1)
(first (rest L1))
(rest (rest L1))

;; a list-of-strings is (cons string list-of-strings)
;; or empty

(define GROCERIES (cons "milk" (cons "cookies" (cons "bread" empty))))
(define YOUR-GROCERIES (cons "milk" (cons "cookies" (cons "tea" (cons "bread" empty)))))

;; len: list-of-strings -> number
;; consumes list and produces the number of items in the list
(define (len alos)
  (cond [(empty? alos) 0]
        [else (+ 1 (len (rest alos)))]))

(check-expect (len GROCERIES) 3)
(check-expect (len empty) 0)

;; contains-tea? list-of-strings -> boolean
;; consumes list and determines if it has "tea" in it
(define (contains-tea? alos)
  (cond [(empty? alos) false]
        [else (or (string=? "tea" (first alos))
                  (contains-tea? (rest alos)))]))

(check-expect (contains-tea? GROCERIES) false)
(check-expect (contains-tea? YOUR-GROCERIES) true)

;; template for functions over list-of-strings 
;;(define (los-template a-los) 
;;  (cond [(empty? a-los) ...]
;;        [else ... (first a-los) 
;;              ... (rest a-los) ...]))