anchor.diff:                    (with-ps-gensyms (n)
                       (let ((decls nil) (assigns nil) (defaults nil))
                         (mapc (lambda (k)
  -                              (multiple-value-bind (var init-form keyword-str)
  +                              (multiple-value-bind (var init-form keyword-str suppl)
                                     (parse-key-spec k)
                                   (push `(var ,var) decls)
                                   (push `(,keyword-str (setf ,var (aref arguments (1+ ,n)))) assigns)
  -                                (push (list 'defaultf var init-form) defaults)))
  +                                (push (list 'defaultf var init-form suppl) defaults)))
                               (reverse keys))
                         `(,@decls
                           (loop :for ,n :from ,(length requireds)
  
positive.code:   (values (if (symbolp spec) spec (first spec))
            (when (listp spec) (second spec))))
  
  (defpsmacro defaultf (place value)
    `(when (=== ,place undefined)
       (setf ,place ,value)))
  
  (defun parse-extended-function (lambda-list body &optional name)
    "Returns two values: the effective arguments and body for a function with
  
negative.code:   ;; list of variable names, and you have access to the arguments variable inside the function:
    ;; * standard variables are the mapped directly into the js-lambda list
    ;; * optional variables' variable names are mapped directly into the lambda list,
    ;;   and for each optional variable with name v, default value d, and
    ;;   supplied-p parameter s, a form is produced (defaultf v d s)
    ;; * keyword variables are not included in the js-lambda list, but instead are
    ;;   obtained from the magic js ARGUMENTS pseudo-array. Code assigning values to
    ;;   keyword vars is prepended to the body of the function. Defaults and supplied-p
    ;;   are handled using the same mechanism as with optional vars.
    (declare (ignore name))
    (multiple-value-bind (requireds optionals rest? rest keys? keys allow? aux? aux
                                    more? more-context more-count key-object)
  