(macro make-encapsulation
  (lambda (body)
    (let ((parameters (cadr body))
          (variables (caddr body))
          (local-procedures (cadddr body))
          (methods (car (cddddr body))))
      `(lambda ,parameters
         (let* ,variables
           (letrec ,(append local-procedures methods)
             (let ((list-of-methods
                     (list . ,(map (lambda (x) `(cons ',(car x) ,(car x)))
                                   methods))))
               (lambda (message)
                 (let ((method (assq message list-of-methods)))
                   (if (null? method)
                       (error "no such method in this encapsulation: " message)
                       (cdr method)))))))))))

(macro old-use-methods
  (lambda (body)
    `(let ,(map (lambda (x)
                  (if (pair? x)
                      `(,(car x) (,(cadr body) ',(cadr x)))
                      `(,x (,(cadr body) ',x))))
                (caddr body))
       . ,(cdddr body))))

(macro use-methods
  (lambda (body)
    (define (clause-parser clause)
      (map (lambda (x)
                  (if (pair? x)
                      `(,(car x) (,(car clause) ',(cadr x)))
                      `(,x (,(car clause) ',x))))
                (cadr clause)))
    `(let ,(map-append! clause-parser (cadr body))
       . ,(cddr body))))

(define (make-encapsulation-iterator encapsulation)
  (let ((pop! (encapsulation 'pop!))
        (empty? (encapsulation 'empty?)))
    (lambda (function)
      (do ()
          ((empty?))
          (function (pop!))))))