anchor.diff:                   (:dynamic
                     (eval-call (get-symbol-value f) (eval-args (cdr form) env)))
                    (:macro (eval-macroexpand (sym-value f) form env))
  -                 (T (error-undeclared-variable f)))
  +                 (T (if (eq :unbound (sym-value f))
  +                      (error-unbound-variable f)
  +                      (eval-call (sym-value f) (eval-args (cdr form) env)))))
                  (ecase (second var)
                    (:dynamic
                     (eval-call (get-symbol-value f) (eval-args (cdr form) env)))
  
positive.code:   (eval-call (sym-value [signal-error])
               (list (sym-value [unbound-variable]) symbol)))
  
  (defun error-undeclared-variable (symbol)
    (eval-call (sym-value [signal-error])
               (list (sym-value [undeclared-variable]) symbol)))
  
  (defun error-constant-modification (symbol)
    (eval-call (sym-value [signal-error])
               (list (sym-value [constant-modification]) symbol)))
  
negative.code:         (:dynamic (get-symbol-value symbol))
          ((:static :constant) (sym-value symbol))
          (:macro (eval-form (sym-value symbol) env))
          (T (if (eq :unbound (sym-value symbol))
               (error-unbound-variable symbol)
               (sym-value symbol))))
        (ecase (second var)
          (:dynamic (get-symbol-value symbol))   
          (:macro (eval-form (cddr symbol) env))
  