#!/usr/bin/perl -w

# File: tk-callback
# Mark Overmeer, AT Computing bv, The Netherlands
# Example for YAPC::Europe 2001

# This program demonstrates callbacks.  It is not easy to construct
# the right syntax.  You can try different options by removing some #'s

use strict;
use Tk;

my $mw     = MainWindow->new;
my $canvas = $mw->Canvas->pack;
my $line   = $canvas->createLine(10,10, 90,90);

my ($x, $y) = (15,10);
$mw->Entry(-textvariable => \$x)->pack;
$mw->Entry(-textvariable => \$y)->pack;

$mw->Button( -text    => 'move'

#          , -command => $canvas->move($line, $x, $y)
# Performed immediately, even before button is created.  The returned
# canvas is assigned as command.  Must be wrong!

           , -command => sub {$canvas->move($line, $x, $y)}
# Uses the current value of $line, $x, and $y when the button
# is clicked.  The variables are kept alive, even when the variables
# get out of scope!

#          , -command => [ 'move', $canvas, $line, $x, $y ]
# Calls $canvas->move('t0', 15, 10), because all values are taken on
# moment of declaration.

#          , -command => [ sub {$canvas->move($line, @_)}, $x, $y ]
# $line is inserted when this line is run, but it will always move
# over 15,10.

           )->pack;

MainLoop;