1 ;; Exercise 3.22.  Instead of representing a queue as a pair of pointers, we can build a queue as a procedure with local state. The local state will consist of pointers to the beginning and the end of an ordinary list. Thus, the make-queue procedure will have the form
2 
3 (define (make-queue)
4   (let ((front-ptr ...)
5         (rear-ptr ...))
6     <definitions of internal procedures>
7     (define (dispatch m) ...)
8     dispatch))
9 
10 ;; Complete the definition of make-queue and provide implementations of the queue operations using this representation.