anchor.diff:            `(-> (,(car rest) ,first) ,@(cdr rest)))
         first))
   
  +(defmacro tee (first &body rest)
  +  "Tee for the threading macro.  Insert first into the first position in each
  +of the body forms, then collect the results as a list."
  +  `(list ,@(mapcar (lambda (form)
  +                     `(-> ,first ,form))
  +                   rest)))
  +
  +(defmacro tap (first form)
  +  "Tap for the threading macro.  Insert first into the first position in form,
  +then return first."
  +  `(progn
  +     (-> ,first ,form)
  +     ,first))
  +
   (defmacro rmapcar (lst fn)
     "Mapcar with arguments reversed.  Allows use with threading macro."
     `(mapcar ,fn ,lst))
  
positive.code:       (setf (cdr (assoc key obj)) value)
        (nconc obj (list (cons key value)))))
  
  (defmethod mset (obj key value)
    (:documentation "Return a mapping with value associated with key.  Don't modify the original mapping."))
  
  (defmethod mset ((obj list) key value)
  
negative.code:   "Shorthand for let for a single binding."
    `(let ((,var ,val))
       ,@body))
  
  (defun <> (&rest strings)
    "Shorthand for concatenating strings."
    (apply #'concatenate (cons 'string strings)))
  