(define make-type
  (let ((type-id 0))
    (lambda (name)
      (set! type-id (+ 1 type-id))
      (cons type-id name))))

(define make-typed-object
  (lambda (type value)
    (cons type value)))

(define typed-object-value
  (lambda (type object)
    (if (eq? type (car object))
        (cdr object)
        (error "type mismatch"))))

(define typed-object-predicate
  (lambda (type)
    (lambda (value)
      (and (pair? value)
           (eq? type (car value))))))