#!/usr/local/bin/perl -w
use Tk;
use strict;

require Tk::TFrame;
require Tk::Adjuster;

my ( $mw, $frmLeft, $adjMiddle, $frmRight, );

$mw = MainWindow->new( -title => 'foo' );

$frmLeft = $mw->TFrame(
    label => [ -text => 'links' ]

)->pack( -expand => 1, -fill => "both", -side => 'left' );

$adjMiddle = $mw->Adjuster(
    -widget  => $frmLeft,
    -side    => 'left',
    -restore => 1,

)->pack( -side => 'left', -fill => 'y' );

$frmRight = $mw->TFrame(
    label => [ -text => 'rechts' ]

)->pack( -expand => 1, -fill => "both", -side => 'right' );

######  Added bit ###################################

$mw->update;

my ( $mw_width, $ratio );

$mw->bind( $mw, '<ButtonRelease-1>' => sub { undef $ratio } );

$mw->bind( $mw,
    '<Configure>' => sub {
        $mw->XEvent;
        my $width = $mw->width;
        $mw_width = $width unless $mw_width;
        if ( $width != $mw_width ) {
            $ratio =
              ( $frmLeft->cget( -borderwidth ) + $frmLeft->width +
                  $adjMiddle->width / 2 ) / $mw_width
              unless $ratio;
            $frmLeft->configure( -width => int( $width * $ratio ) );
            $mw_width = $width;
        }
    }
);

$mw->eventGenerate('<Configure>');

#######################################################

MainLoop;