yafolding-custom-collapse.el

(defun should-collapse-p ()
  (string-match-p "\s-*(def.*"
                  (buffer-substring-no-properties
                   (line-beginning-position)
                   (line-end-position))))


(defun open-by-controller (should-collapse-p)
  (let* ((region (yafolding-get-element-region))
         (beg (car region))
         (end (cadr region)))
    (save-excursion
      (next-line)
      (while (< (point) (+ 1 end))
        (when (should-collapse-p)
          (yafolding-hide-element))
        (next-line)))))

;; (open-by-controller 'should-collapse-p)