I'm learning Racket and have implemented a mutable stack, which is just a bunch of wrappers around an underlying struct containing a size and buffer list (so it's not optimal, in terms of computational complexity). After consulting #racket and reading the first half of Greg Hendershott's Fear of Macros, I was able to write the syntax transformations I wanted for my implementation.

(module stack racket
  (module stack-implementation racket
    (struct stack (size buffer) #:mutable)

    ;; size :: stack -> integer
    (define (size stack) (stack-size stack))

    ;; non-empty-stack? :: stack -> boolean
    (define (non-empty-stack? stack)
      (and
        (stack? stack)
        (positive? (stack-size stack))))

    ;; push! :: stack -> any (new item) -> integer (size)
    (define (push! stack item)
      (set-stack-buffer! stack
        (append (list item) (stack-buffer stack)))

      (set-stack-size! stack (+ (stack-size stack) 1))

      (stack-size stack))

    ;; pop! :: (non-empty) stack -> any (head)
    (define (pop! stack)
      (let ([head (car (stack-buffer stack))]
            [tail (cdr (stack-buffer stack))])

        (set-stack-buffer! stack tail)
        (set-stack-size! stack (- (stack-size stack) 1))

        head))

    ;; make
    (define-syntax-rule (make name)
      (define name (stack 0 '())))

    (provide make
             stack?
             (contract-out
               [size  (-> stack?            integer?)]
               [push! (-> stack? any/c      integer?)]
               [pop!  (-> non-empty-stack?  any)])))

  (require 'stack-implementation
           (for-syntax racket/syntax))
  
  ;; make-stack
  ;  Defines a stack under the specified symbol <name>
  ;  Plus defines <name>-size, <name>-empty?, <name>-push! and <name>-pop!
  (define-syntax (make-stack stx)
    (syntax-case stx ()
      [(_ name)
        (with-syntax ([(size-fn empty-fn push-fn pop-fn)
                       (map (lambda (fn) (format-id stx "~a-~a" #'name fn))
                            '("size" "empty?" "push!" "pop!"))])
          #'(begin
              (make name)
              (define (size-fn)      (size name))
              (define (empty-fn)     (zero? (size-fn)))
              (define (push-fn item) (push! name item))
              (define (pop-fn)       (pop!  name))))]))

  (provide make-stack
           stack?))

I'm completely new to Racket and Lisp, so I'm guessing there are many improvements I can make here (e.g., the duplication in the macro where I define the helper function IDs), besides using a better underlying data structure.