Vorlesung 2 Grüning

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Archivierte Version vom 2021-03-26T13:38:10+00:00. Aktuelle Version

Hilbert Hotel

(define stream-car car)

(define stream-cdr
  (lambda (stm)
    (force (cdr stm))))

(define-macro (stream-cons head tail)
  `(cons ,head (delay ,tail)))

(define stream?
  (lambda (stm)
    (and (pair? stm) (promise? (cdr stm)))))

(define stream-map
  (lambda (proz stm)
    (stream-cons (proz (stream-car stm)) (stream-map proz (stream-cdr stm)))))

(define show-stream
  (lambda (stm n)
    (letrec
        ([show
          (lambda (stm n ls)
            (if (= n 0)
                (apply display (append ls (list "...")))
                (show (stream-cdr stm) (- n 1) (append ls (list (stream-car stm) ", ")))))])
      (show stm n ()))))

(define zeige-mir show-stream)

(define baue-hilberthotel
  (lambda ()
    (stream-cons #f (baue-hilberthotel)))
  )

(define hilberthotel (baue-hilberthotel))

(zeige-mir hilberthotel 11)

(define einzelbuchung
  (lambda (val stm pos)
    (letrec
        ([shorten
          (lambda (val stm pos)
            (if (= pos 0)
                (stream-cons val (stream-cdr stm))
                (stream-cons (stream-car stm) (shorten val (stream-cdr stm) (- pos 1)))
                ))
          ])
    (shorten val stm pos)
      )
    )
  )

(set! hilberthotel (einzelbuchung "Otto Grundmann" hilberthotel 3))
(zeig-mir hilberthotel 12)

Vorlesung 2 Grüning

Hilbert Hotel

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