anchor.diff:                  root
                   (compute-ptree root ptree (check-kernel)))))))))
   
  -(defun has-lambda-list-keyword-p (list)
  -  (some (lambda (elem) (find elem lambda-list-keywords)) list))
  -
   (defmacro ptree (defs &body body)
     "Create a ptree using `flet' syntax.
   
  
positive.code:       (declare (ignore forms))
        (check-type id symbol)
        (check-type args list)
        (when-let (keyword (has-lambda-list-keyword-p args))
          (error 'ptree-lambda-list-keyword-error
                 :id id
                 :keyword keyword))))
    (with-gensyms (tree)
      `(let ((,tree (make-ptree)))
         ,@(loop
  
negative.code:    "Attempted to execute a node which had no function."))
  
  (define-condition ptree-lambda-list-keyword-error (ptree-error)
    ((llks :initarg :llks :reader ptree-error-llks))
    (:report
     (lambda (err stream)
       (format stream
               "Function arguments in `ptree' cannot contain lambda list ~
                keywords.~%In definition of ~a found: ~{~s~^ ~}"
               (ptree-error-id err)
               (ptree-error-llks err))))
    (:documentation
     "Lambda list keywords found in function definition."))
  
  