my @part = (
	'http://example.net/app',
	( 'admin'          ? $is_admin_link : () ),
	( defined $subsite ? $subsite       : () ),
	$mode,
	( defined $id      ? $id            : () ),
	( defined $submode ? $submode       : () ),
);

my $uri = join '/', @part;

##</code><code>##

my @part = map defined $_->[-1] ? $_->[0] : (), 
  ['http://example.net/app' => 1],
  ['admin' => $is_admin_link],
  [$subsite], [$mode => 1], [$id], [$submode];

##</code><code>##

my @part = map +(ref) ? (defined $_->[-1] ? $_->[0] : ()) : $_, 
  'http://example.net/app',
  ['admin' => $is_admin_link],
  [$subsite], $mode, [$id], [$submode];