thanks tybalt89 for you working example: it turned out i was looking at the wrong part of Mastering Perl Tk book (chapter 13.22. Time Delays contains useful informations: i was on Anatomy of MainLoop).

My problem with ?: was the worst Perl gaffe by me since years..

You should never sleep() in a Tk program. I suspected this, and sounds like a good motto. It reminds me to an older one dormitare cogitantem de fuga vetat that translates more or less in: to sleep is forbidden to those plaining an escape

L*