(define make-buffer
  (lambda (_capacity)
    (let ((contents (make-vector _capacity))
          (front 0)
          (back 0)
          (capacity _capacity)
          (size 0))
      (lambda (command . params)
        (cond 
          ((eq? command ':empty?)
           (<= size 0))
          ((eq? command ':full?)
           (>= size capacity))
          ((eq? command ':get!)
           (let ((tmp (vector-ref contents front)))
              (set! front (modulo (+ front 1) capacity))
              (set! size (- size 1))
              tmp))
          ((eq? command ':put!)
           (vector-set! contents back (car params))
           (set! back (modulo (+ back 1) capacity))
           (set! size (+ size 1)))
          ((eq? command ':dump)
           (display "capacity: ") (display capacity) (newline)
           (display "size: ") (display size) (newline)
           (display "front: ") (display front) (newline)
           (display "back: ") (display back) (newline)
           (display "contents: ") (display contents) (newline))
          (else
            (error "Undefined command")))))))