anchor.diff:  
   (defun function? (x)
     "Check whether X is a function."
  -  (= (type x) "function"))
  +  (or (= (type x) "function")
  +      ; HACK: We pretend that multimethods are functions.
  +      (= (type x) "multimethod")))
   
   (defun key? (x)
     "Check whether X is a key."
  
positive.code:       (set! out `(,(.. (pretty k) " " (pretty v)) ,@out)))
      (.. "{" (.. (concat out " ") "}"))))
  
  (defdefault pretty (x)
    (tostring x))
  
  
negative.code:       (set! n (+ 1 n))
        (set-idx! out n k))
      (set-idx! out :n n)
      out))
  
  (defun s->s (x) :hidden (get-idx x :contents))
  
  