#!/usr/bin/env perl

use strict;
use warnings;

use Tk;

my $tissue = 'plasma';

my $mw = MainWindow->new;

my $f1 = $mw->Frame()->pack;
$f1->Label(-textvariable => \$tissue)->pack;
$f1->Button(-text => 'Select Tissue', -command => sub { select_tissue(\$tissue) })->pack;
$f1->Button(-text => 'Quit', -command => sub { do_end(\$tissue) })->pack;

MainLoop;

sub select_tissue {
    my $tissue_ref = shift;
    # Tissue selection code here - assume 'muscle' selected
    $$tissue_ref = 'muscle';
    return;
}

sub do_end {
    my $tissue_ref = shift;
    # Print to STDOUT for demo purposes
    print "$$tissue_ref\n";
    exit;
}