Would like to specify multiple tags

.emacs

(defvar journal-site-location "~/journal/"
  "The location of the journal files.")

(defun journal-new-post (title tags yyyy mm dd)
  "Create a new journal post for today with TITLE and TAG."
  (interactive (list
                (read-string "Title: ")
                (journal-read-tags)
                (read-string (format "Year (%s): " (format-time-string "%Y")) nil nil (format-time-string "%Y"))
                (read-string (format "Month (%s): " (format-time-string "%m")) nil nil (format-time-string "%m"))
                (read-string (format "Date (%s): " (format-time-string "%d")) nil nil (format-time-string "%d"))
                )
               )
  (let (
        (file-name (journal-post-title dd title))
        (file-path (journal-post-path title yyyy mm dd))
        )
    (set-buffer (get-buffer-create file-path))
    (insert
     (format "---\ntitle: %s\ntags: [ %s, \"\" ]\nauthor: Rob Nugen\ndate: %s-%s-%sT%s\n---\n\n%s\n\n"
             title
             (mapconcat (lambda (x) (format "\"%s\"" (downcase x)))
                   tags ", ")
             yyyy
             mm
             dd
             (format-time-string "%H:%M:%S+09:00")
             (format-time-string "## %H:%M %A %d %B %Y %Z")
             ))
    (write-file
     (expand-file-name file-path (concat journal-site-location "")))
    (switch-to-buffer file-name)
    (auto-fill-mode)
  )
)

(defun journal-read-tags ()
  (let (tags tag done)
    (while (not done)
      (setq tag (read-string "Tag: "))
      (if (= (length tag) 0)
          (setq done t)
        (push tag tags)))
    (nreverse tags)))

(defun journal-post-title (dd title)
  "Return a file name based on TITLE for the post."
  (concat dd
   (url-safe-string title)
   ".md"))

(defun url-safe-string (title)
  "Return a URL-safe title based on TITLE."
  (replace-regexp-in-string "[:!']" ""
    (replace-regexp-in-string " " "-" (downcase title))
    )
  )

(defun journal-post-path (title yyyy mm dd)
  "Return a file path based on TITLE and date."
  (concat
   yyyy "/" mm "/" dd
   (url-safe-string title)
   ".md"))


(global-set-key (kbd "C-c j") 'journal-new-post)