sample($t,0);

sub sample {
	my $t = shift;
	my $index = shift;
	my ($p, @r, $v, $rt);
	$t->get_handles(params=>\$p, rtrs=>\@r, vars=>\$v, t=>\$rt);
	
	my @subs;
	if (defined $index) {
		my $rh = $r[$index];
		<some command at execution>
	}
	else {
		foreach my $rh (@r) {
			<some command at execution>
			...
		}
	}
}