;; 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 phone-book) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
(define-struct pair (name num))
;;An Entry is a (make-pair String Number)

(define e1 (make-pair "bob" 123))
(define e2 (make-pair "alice" 456))
(define e3 (make-pair "carol" 789))

;;A LOE [list of Entry] is one of
;; - empty
;; - (cons Entry LOE)

(define pb (cons e1 (cons e2 (cons e3 empty))))
(define pb2 (cons e1 (cons e2 (cons e3 (cons e1 empty)))))

;;LOE String -> LOE
;;remove the contact with the given name from the phone-book
(define (remove-e aloe str)
  (cond
    [(empty? aloe) empty]
    [(cons? aloe) (if (name-checker (first aloe) str)
                      (remove-e (rest aloe) str)
                      (cons (first aloe) (remove-e (rest aloe) str)))]))

(check-expect (remove-e pb "bob")
              (cons e2 (cons e3 empty)))
(check-expect (remove-e empty "bob") empty)
(check-expect (remove-e pb "billy") pb)
(check-expect (remove-e pb2 "bob") 
              (cons e2 (cons e3 empty)))

;;Entry String -> Boolean 
;;check if the name in the Entry matches the given string
(define (name-checker an-e str)
  (string=? (pair-name an-e) str))
  
(check-expect (name-checker e1 "bob") true)
(check-expect (name-checker e2 "bob") false)