Yeah, see Re: Perk Tk - how to send a value from a subroutine back to the main program using Button (without MainLoop), see what MainLoop does is this

sub MainLoop
{
 unless ($inMainLoop)
  {
   local $inMainLoop = 1;
   while (Tk::MainWindow->Count)
    {
     DoOneEvent(0);
    }
  }
}
[download]

You move the mouse, its an event (a bunch)

You click a button, its an event

Nothing happens for a few miliseconds, its an event

If you use Tk::Wizard then each page you add, each wizard step, is like a separate MainLoop, and then returning a value can be possible (you can write procedural code), see the examples