(load "queue.txt")

; 1 ]=> (define q1 (make-queue))
; 
; ;Value: q1
; 
; 1 ]=> (insert-queue! q1 'a)
; 
; ;Value: ((a) a)
; 
; 1 ]=> (insert-queue! q1 'b)
; 
; ;Value: ((a b) b)
; 
; 1 ]=> (delete-queue! q1)
; 
; ;Value: ((b) b)
; 
; 1 ]=> (delete-queue! q1)
; 
; ;Value: (() b)

; The evaluator is printing the queue like a pair with a list as the first
; element and an atom as the second, because that is the internal
; representation hidden behind the queue abstraction. The reason the last
; queue element appears twice in the output is because the rear pointer points
; into the list the front pointer points to. The interpreter will print the
; list of elements and then follow the rear pointer which points to an already
; printed element.

; Because the interpreter does not understand the meaning of the queue
; internals, we must program our own print function which takes into account
; the meaning of the queue internals.

(define (print-queue queue)
  (display (front-ptr queue)))