;; Die ersten drei Zeilen dieser Datei wurden von DrRacket eingefügt. Sie enthalten Metadaten
;; über die Sprachebene dieser Datei in einer Form, die DrRacket verarbeiten kann.
#reader(lib "DMdA-assignments-reader.ss" "deinprogramm")((modname account) (read-case-sensitive #f) (teachpacks ()) (deinprogramm-settings #(#f write repeating-decimal #t #t none explicit #f ())))
; Aktueller Kontostand
(: balance natural)
(define balance 130)

;(: withdraw (natural -> natural))
#;(define withdraw
  (lambda (amount)
    (if (>= balance amount)
        (begin (set! balance (- balance amount))
               balance)
        (violation "No money!"))))

; Konto abheben mit lokalen Zustand
(define new-withdraw
  (letrec ((balance 130))
    (lambda (amount)
      (if (>= balance amount)
          (begin (set! balance (- balance amount))
                 balance)
          (violation "No money!")))))

; Konto mit einem gegebenen Kontostand erzeugen.
(: make-withdraw (natural -> (natural -> natural)))
(define make-withdraw
  (lambda (balance)
    (lambda (amount)
      (if (>= balance amount)
          (begin (set! balance (- balance amount))
                 balance)
          (violation "No money!")))))

(: A1 (natural -> natural))
(define A1 (make-withdraw 130))

(: A2 (natural -> natural))
(define A2 (make-withdraw 130))

(define account-message
  (signature (one-of "withdraw" "deposit")))

(: make-account (natural -> (account-message -> (natural -> natural))))
(define make-account
  (lambda (init-amount)
    (letrec ((balance init-amount)
             
             (withdraw
              (lambda (amount)
                (if (>= balance amount)
                    (begin (set! balance (- balance amount))
                           balance)
                    (violation "No money!"))))
             
              (deposit
               (lambda (amount)
                 (begin (set! balance (+ balance amount))
                        balance)))
              
              (dispatch
               (lambda (message)
                 (cond ((string=? message "withdraw") withdraw)
                       ((string=? message "deposit" ) deposit)))))
      
      dispatch)))

(define acct (make-account 100))