anchor.diff:       (make-clutter-operator
         :function (lambda (*denv* values)
                     (cadr values)))))
  +
   (defprimitive list (make-function
                       (make-clutter-operator
                        :function (lambda (*denv* values)
  
positive.code:      (make-clutter-operator
        :function (lambda (*denv* values)
                    (reduce #'+ values)))))
  (defprimitive car
      (make-function
       (make-clutter-operator
  
negative.code:         (t expression)))
  
  (defun eval/symbol (symbol env)
    (if (keywordp symbol)
        symbol
        (let ((val (lookup symbol env)))
          (if (clutter-symbol-operator-p val)
              (invoke (clutter-symbol-operator-operator val) env nil)
              val))))
  
  (defun eval/combiner (expression env)
    (let ((f (clutter-eval (car expression) env)))
  