You define the Tcl 'bgerror' function in the if you want to override this. The Tkx API does not provide a direct way to do this if you want the bgerror command to be a perl function, so this example shows a possible workaround:

#!perl -w

use strict;
use warnings;
use Tkx;

Tkx::button(".b",
     -text => "Hello, world",
     -command => sub { Tkx::foo(); },  # XXX will fail
);
Tkx::pack(".b");

Tkx::set("perl_bgerror", sub {
     splice(@_, 0, 3);  # skip internal callback junk
     my $msg = shift;
     print "Error: $msg\n";
});

Tkx::eval(<<'EOT');
proc bgerror {msg} {
      global perl_bgerror
      $perl_bgerror $msg
}
EOT

Tkx::MainLoop()

__END__
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