anchor.diff:  (defun precedence (e)
     (etypecase e
       (cgen-op (op-precedence (cgen-op-op e)))
  -    (number 99)
  -    (rope 99)))
  +    (number 0)
  +    (rope 0)))
   
   (defun cgen-op-symbol (op)
     "Return the canonical symbol of op"
  
positive.code:               ((:band) '&)
                ((:= =) '=)
                (otherwise op))))
      (op-precedence op)
      op))
  
  
  
negative.code: (defun cgen-parenthesize (parent child)
    ;(format t "~&parent: ~A:~D" parent (precedence parent))
    ;(format t "~&child: ~A:~D" child (precedence child))
    (if (> (precedence child) (precedence parent))
        (rope-parenthesize child)
        (rope child)))
  
  