First, Tk::repeat is a quick shortcut for Tk::after, read "perldoc Tk::after". Look thru Tk::after's methods to see if there is something you can use. Second, you didn't show a complete code example, but with Tk timers, if you declare them BEFORE you create them, you can use their variable name within the callback, like:

#pseudocode

my $timer;
# code update line below, I forgot to define $timer
$timer = $mw->repeat( 50, {    #you can use $timer here   
                                 if $whatever, $timer->cancel;
                              }  );    
# declare outside the callback, otherwise a $timer cannot cancel itsel
+f
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If you really want to get into a select style usage, within Tk, it dosn't work well, because it will interfere with the eventloop. But there is a workaround. See Tk::Trace in Simple Tk Gauge