I am trying to make my first steps with ltk, and I have problems to reconfigure existing widgets. Here is an example where I try to reconfigure the :TEXT attribute of the LABEL-WIDGET widget whenever the checkbox of the CHECK-BUTTON-WIDGET widget is clicked.
Try with setf instead of configure, i.e. (setf (text label-widget) val) instead of (configure label-widget :text val)
Sincerely, Harven