anchor.diff:              (unless (find-binding name fenv)
                 (error "~A is not a lexically visible function" name))
               (lookup name fenv)))
  +         (|var|
  +          (destructuring-bind (name)
  +              argument-forms
  +            ;; Sanity checks -- these should happen at "compile time"
  +            (unless (symbolp name)
  +              (error "~A is not a valid variable name." name))
  +            (unless (find-binding name env)
  +              (error "~A is not a visible variable." name))
  +            (lookup name env)))
            (|bind-lexical-functions|
             (destructuring-bind (vars-and-funs &body body)
                 argument-forms
  
positive.code:           (destructuring-bind ((&rest args) &body body)
                argument-forms
              (make-function args body env fenv)))
           (|function|
            (destructuring-bind (name)
                argument-forms
              ;; Sanity checks -- these should happen at "compile time"
  
negative.code:      (destructuring-bind (operator &rest argument-forms) form
  
         ;; Sanity check -- this should happen at "compile time"
         (unless (or (symbolp operator) (listp operator))
           (error "~A is not a valid operator." (car form)))
  
         ;; Special operators
         (case operator
  