...a doubt rised about the "waitVariable" method is that I suspect that if the timer of repeat is too small, the repeat could set the variable before the creation of waitVariable object and the program could block:

sub xyz{
  $wid->repeat(1, sub{ $var=1; } ); # after 1 millisecond $var==1
  # 1 ms... 2ms... 3ms...
}

{
  &xyz;
  # 6 ms... 7ms... 8ms...
  $widget->waitVariable(\$var); # will this wait indefinitely because 
+the var was already changed???
  # Continue... never will happen
}
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It depends on how repeat works (I don't know); but because it returns before the first pause (see Tk::after documentation) should be possible to do a sufficient reliable use of waitVariables, even if this appears to me like a bad patch...