anchor.diff:    (if (isource-array-slot-p hidden-slot)
         `(defun ,original-slot-name (input-source index)
            (ensure-n-long (,(first hidden-slot) input-source)
  -                          (+ index 1)
  -                          (,(control-constructor-name control-type)))
  +                        (+ index 1)
  +                        (,(control-constructor-name control-type)))
            (,(control-data-acc-name control-type)
              (aref (,(first hidden-slot) input-source) index)))
         `(defun ,original-slot-name (input-source)
  
positive.code:        ;; Type
         (,def (,name (:constructor ,constructor)
                      (:conc-name nil))
           ,@(mapcar #'gen-struct-slot-from-input-source-slot hidden-slots))
  
         ;; public constructor
         (defun ,(input-source-constructor-name name) ()
  
negative.code:                 :for slot-name :in hidden-slot-names :collect
                  (let ((kwd (intern (symbol-name cname) :keyword))
                        (msg0 (format nil "SKITTER: ~a in ~a is a array of ~a"
                                      cname name type))
                        (msg1 (format nil "SKITTER: ~a in ~a is not an array of controls. No index is required"
                                      cname name)))
                    (if length
                        `(,kwd
                          (cond
  