SICP/ex-3_21-23.scm

(load "shared/util.scm")

(display "\nexample - queue\n")

(define (front-ptr queue) (car queue))
(define (rear-ptr queue) (cdr queue))
(define (set-front-ptr! queue item) (set-car! queue item))
(define (set-rear-ptr! queue item) (set-cdr! queue item))

(define (empty-queue? queue) (null? (front-ptr queue)))

(define (make-queue) (cons '() '()))
(define (front-queue queue)
  (if (empty-queue? queue)
      (error "FRONT called with an empty queue" queue)
      (car (front-ptr queue))))

(define (insert-queue! queue item)
  (let ((new-pair (cons item '())))
    (cond ((empty-queue? queue)
           (set-front-ptr! queue new-pair)
           (set-rear-ptr! queue new-pair)
           queue)
          (else
           (set-cdr! (rear-ptr queue) new-pair)
           (set-rear-ptr! queue new-pair)
           queue))))

(define (delete-queue! queue)
  (cond ((empty-queue? queue)
         (error "DELETE! called with an empty queue" queue))
        (else
         (set-front-ptr! queue (cdr (front-ptr queue)))
         queue)))

(define q (make-queue))
(insert-queue! q 'a)
(insert-queue! q 'b)
(delete-queue! q)
(insert-queue! q 'c)
(insert-queue! q 'd)
(delete-queue! q)

(display "\nex-3.21 - print queue\n")

(define print-queue front-ptr)

(define q1 (make-queue))
(assert (print-queue (insert-queue! q1 'a)) '(a))
(assert (print-queue (insert-queue! q1 'b)) '(a b))
(assert (print-queue (delete-queue! q1)) '(b))
(assert (print-queue (delete-queue! q1)) '())


(display "\nex-3.22 - procedural queue\n")

(define (make-queue)
  (let ((front-ptr '())
        (rear-ptr '()))
    (define (empty-queue?) (null? front-ptr))
    (define (insert-queue! item)
      (let ((new-pair (cons item '())))
        (cond ((empty-queue?)
               (set! front-ptr new-pair)
               (set! rear-ptr new-pair)
               dispatch)
              (else
               (set-cdr! rear-ptr new-pair)
               (set! rear-ptr new-pair)
               dispatch))))
    (define (delete-queue!)
      (cond ((empty-queue?)
             (error "DELETE! called with an empty queue" queue))
            (else
             (set! front-ptr (cdr front-ptr))
             dispatch)))
    (define (dispatch m)
      (cond
        ((eq? m 'insert) insert-queue!)
        ((eq? m 'delete) delete-queue!)
        ((eq? m 'print) (lambda () front-ptr))
        (else (error "Undefined operation -- DISPATCH-QUEUE" m))))
    dispatch)))

(define q (make-queue))
((q 'insert) 'a)
((q 'insert) 'b)
((q 'insert) 'c)
((q 'insert) 'd)
(assert ((q 'print)) '(a b c d))
((q 'delete))
((q 'delete))
(assert ((q 'print)) '(c d))

(display "\nex-3.23 - deque\n")

; A deque (``double-ended queue'') is a sequence in which items can be inserted
; and deleted at either the front or the rear.  Show how to represent deques
; using pairs, and give implementations of the operations.23 All operations
; should be accomplished in (1) steps.

(define (front-ptr deque) (car deque))
(define (rear-ptr deque) (cdr deque))
(define (set-front-ptr! queue item) (set-car! queue item))
(define (set-rear-ptr! queue item) (set-cdr! queue item))

(define (make-deque) (cons '() '()))
(define (empty-deque? deque) (null? (front-ptr deque)))

(define (make-node item prev-ptr next-ptr)
  (cons item (cons prev-ptr next-ptr)))

(define (set-prev-node! node prev-ptr)
  (set-car! (cdr node) prev-ptr))

(define (set-next-node! node next-ptr)
  (set-cdr! (cdr node) next-ptr))

(define (prev-node node) (car (cdr node)))
(define (next-node node) (cdr (cdr node)))

(define (display-deque deque)
  (define (iter-nodes node)
    (if (null? node)
      'done
      (begin
        (display (car node))
        (if (null? (next-node node))
          'do-nothing
          (display ", "))
        (iter-nodes (next-node node)))))
  (display "[")
  (iter-nodes (front-ptr deque))
  (display "]\n"))

(define (front-deque deque)
  (if (empty-deque? deque)
    (error "FRONT called with an empty deque")
    (car (front-ptr deque))))

(define (rear-deque deque)
  (if (empty-deque? deque)
    (error "REAR called with an empty deque")
    (car (rear-ptr deque))))

(define (front-insert-deque! deque item)
  (let ((new-node (make-node item '() '())))
    (cond ((empty-deque? deque)
           (set-front-ptr! deque new-node)
           (set-rear-ptr! deque new-node)
           deque)
          (else
            (set-next-node! new-node (front-ptr deque))
            (set-prev-node! (front-ptr deque) new-node)
            (set-front-ptr! deque new-node)
            deque))))

(define (rear-insert-deque! deque item)
  (let ((new-node (make-node item '() '())))
    (cond ((empty-deque? deque)
           (set-front-ptr! deque new-node)
           (set-rear-ptr! deque new-node)
           deque)
          (else
            (set-prev-node! new-node (rear-ptr deque))
            (set-next-node! (rear-ptr deque) new-node)
            (set-rear-ptr! deque new-node)
            deque))))

(define (front-delete-deque! deque)
  (cond ((empty-deque? deque)
         (error "DELETE! called with an empty deque" deque))
        ((null? (next-node (front-ptr deque)))
         (set-front-ptr! deque '())
         (set-rear-ptr! deque '()))
        (else
         (set-front-ptr! deque (next-node (front-ptr deque)))
         (set-prev-node! (front-ptr deque) '())
         deque)))

(define (rear-delete-deque! deque)
  (cond ((empty-deque? deque)
         (error "DELETE! called with an empty deque" deque))
        ((null? (prev-node (rear-ptr deque)))
         (set-front-ptr! deque '())
         (set-rear-ptr! deque '()))
        (else
         (set-rear-ptr! deque (prev-node (rear-ptr deque)))
         (set-next-node! (rear-ptr deque) '())
         deque)))


(define d (make-deque))
(front-insert-deque! d 3)
(rear-insert-deque! d 4)
(front-insert-deque! d 2)
(rear-insert-deque! d 5)
(front-insert-deque! d 1)
(rear-insert-deque! d 6)
(display-deque d)

(front-delete-deque! d)
(rear-delete-deque! d)
(front-delete-deque! d)
(rear-delete-deque! d)
(front-delete-deque! d)
(rear-delete-deque! d)
(display-deque d)