;; 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-intermediate-lambda-reader.ss" "lang")((modname lab8-starter-file-1) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))
(define-struct user [name friends enemies])
; A SocialNetwork (SN) is a [Listof User].
; A User is a (make-user String [Listof String] [Listof String])
; Interpretation: name is the user's nick name, 
; friends is a list of (the names of) their friends, and
; enemies is a list of (the names of) their enemies.

(define amanda
  (make-user "Amanda" '("Carlo" "Diya" "Fran") '()))
(define bruce
  (make-user "Bruce"
             '("Carlo" "Diya" "Emmi" "Fran" "Han")
             '("Fran" "Diya" "Carlo")))
(define carlo
  (make-user "Carlo" '("Diya" "Han") '("Amanda")))
(define diya
  (make-user "Diya" '("Emmi" "Fran" "Han") '("Fran" "Carlo")))
(define emmi
  (make-user "Emmi"
             '("Fran" "Han")
             '("Carlo" "Diya" "Bruce" "Fran" "Han")))
(define fran
  (make-user "Fran" '("Gregg" "Han") '("Amanda" "Carlo"))) 
(define gregg
  (make-user "Gregg" '() '("Han" "Bruce" "Fran"))) 
(define han
  (make-user "Han" '("Gregg") '("Bruce" "Carlo")))

(define SN1 (list amanda bruce carlo diya emmi fran gregg han))






; LIBRARY FUNCTIONS -----------------------------------------------------------

; drop : String [Listof String] -> [Listof String]
; Remove all occurrences of the given element from the list, if it is present.

(define (drop str los)
  (filter (λ(x) (not (string=? str x))) los))

(check-expect (drop "hi" '()) '())
(check-expect (drop "hello" '("cats" "are not that affectionate"))
              '("cats" "are not that affectionate"))
(check-expect (drop "cats" '("cats" "hi" "i" "still" "love" "cats" "lots"))
              '("hi" "i" "still" "love" "lots"))


; count : String [Listof String] -> Number
; Count how many times the given string appears in the list.

(define (count str los)
  (foldr (λ(x y) (if (string=? str x) (+ y 1) y)) 0 los))

(check-expect (count "hi" '()) 0)
(check-expect (count "hello" '("cats" "are great")) 0)
(check-expect (count "cats" '("cats" "hi" "i" "love" "cats" "lots")) 2)