anchor.diff:  (defclass string-expression ()
     ((string :initarg :string)))
   
  +(defclass namespace ()
  +  ((name :initarg :name)
  +   (declarations :initarg :declarations)))
  +
  +(defclass namespace-declaration ()
  +  ((var :initarg :var)
  +   (value :initarg :value)
  +   (type :initarg :type)
  +   (export-p :initarg :export-p)
  +   (comment :initarg :comment)))
  +
   (defvar *token-iterator*)
   
   (defun next-token ()
  
positive.code:     (make-instance 'interface :elements (nreverse elements))))
  
  (defun parse-def-interface ()
    (accept 'word "export")
    (when (accept 'word "interface")
      (let ((interface-name (token-string (exact 'word)))
            (extends-interface
  
negative.code:   (when (match token-type string)
      (next-token)))
  
  (defun parsing-error ()
    (error "Token not expected: ~S" (ahead-token)))
  
  (defun exact (token-type &optional string)
    (or (accept token-type string)
        (parsing-error)))
  
  (defun parse-type-expression ()
    (labels ((type-name ()
  