uebung7.scm

#lang racket
{define (loesche liste praedikat) ; A33
  [if (praedikat (car liste))
      [if (null? (cdr liste))
          '()
          (loesche (cdr liste) praedikat)
          ]
      liste
      ]
  }

(println "A33")
(loesche (list 4 6 8 3 2 4 5) even?)

{define (drehe liste) ; A34
  {define (iter alt neu)
    [if (null? alt) neu
        (iter (cdr alt) (cons (car alt) neu))
        ]
    }
  (iter liste '())
  }

(println "A34")
(drehe (list 1 2 3))
(drehe (list 1 2 (list 3)))
(drehe (list 1 (list 5 6) 2 (list 3 4)))

{define (typ-or typ1 typ2) ; A35
  (lambda (x) (or (typ1 x) (typ2 x)))
  }

(println "A35")
(define paar-oder-liste? (typ-or pair? list?))
(define integer-oder-boolean? (typ-or integer? boolean?))
(integer-oder-boolean? (paar-oder-liste? (cons 1 2)))


{define (operation operatoren n) ; A36
  [if (= n 1)
      (lambda (x) ((car operatoren) (car x) (cadr x)))
      (operation (cdr operatoren) (- n 1))
      ]
  }

(println "A36")
(define plus (operation (list + - * /) 1))
(plus (list 1 2))
(define minus (operation (list + - * /) 2))
(minus (list 1 2))

{define (caesar_encrypt_list data key) ; A37
  {define (element-at-iter list n)  (list-ref list (remainder n (length list))) }

  {define (iter data new key key-offset)
    [if (null? data)
        new
        (iter (cdr data) (append new (list (remainder (+ (car data) (element-at-iter key key-offset)) 10))) key (+ 1 key-offset))
        ]
    }

  (iter data '() key 0)
  }

(println "A37")
(caesar_encrypt_list (list 1 2 3 4 5 6) (list 1 3 3 7))