anchor.diff:  
   (defvar *history-table* (make-hash-table))
   
  -(define-condition execute ()
  +(define-condition execute-condition ()
     ((input
       :initarg :input
       :reader execute-input)))
  
positive.code:     (when (or (null (prompt-window-existing-test-function (current-prompt-window)))
                (funcall (prompt-window-existing-test-function (current-prompt-window)) input))
        (lem.history:add-history (prompt-window-history (current-prompt-window)) input)
        (error 'execute :input input))))
  
  (define-command prompt-completion () ()
    (alexandria:when-let (completion-fn (prompt-window-completion-function (current-prompt-window)))
  
negative.code:                   (funcall body-function))
              (delete-prompt prompt-window)
              (run-hooks *prompt-deactivate-hook*))
          (execute-condition (e)
            (execute-input e))))))
  
  (defmethod lem::%prompt-for-character (prompt-string &key (gravity :center))
    (prompt-for-aux :prompt-string prompt-string
  