$fh = \*STDOUT;
$filter = sub {
	my $a = shift;
	print "Filtered: $a";
};

print $fh "Hello\n";
print $fh  &{$filter}("Cool");        # Syntax error
#print $fh  "" . &{$filter}("Cool");   # This is fine.
#print $fh  &{$filter}("Cool") . "";   # Syntax error here, too.
#print $fh $filter->("Cool");          # This works, too.