org-feed-update doesn't understand the file name of a target Org-file when it is not a constant

["Евгений Курбатов" <EvgenyKurbatov@yandex.ru>]

Hello!

I do some elisp code to download the latest RSS feeds from some resource:

(setq debug-on-error t)
(org-mode)
(org-feed-update
 '("arxiv"
   "http://export.arxiv.org/rss/astro-ph"
   (concat "~/org/arxiv-" (format-time-string "%Y-%m-%d.org"))
   "arXiv.org"
   )
 )

The goal is to get an unique Org file for feeds per day. However, the error is rising:

Debugger entered--Lisp error: (wrong-type-argument stringp (concat "~/org/arxiv-" (format-time-string "%Y-%m-%d.org")))
  expand-file-name((concat "~/org/arxiv-" (format-time-string "%Y-%m-%d.org")))
  find-file-noselect((concat "~/org/arxiv-" (format-time-string "%Y-%m-%d.org")) nil nil nil)
  find-file((concat "~/org/arxiv-" (format-time-string "%Y-%m-%d.org")))
  org-feed-goto-inbox-internal((concat "~/org/arxiv-" (format-time-string "%Y-%m-%d.org")) "arXiv.org")
  byte-code("\306   \"\307\n\"\310\311
\"\211\312+\211,\203]

When I hardcode a string instead of (concat ...) everything is ok. The subject is also not in format-time-string, it is exactly in concat. The type returned by concat is the stringp, so the situation is very strange. I also tried to use org-feed-alist, and local variable instead of calling concat, nothing helps.

Regards,
Evgeny