print('$|--: '); $|=0; for (1..10) { print($|--, ' '); } print("\n");
print('--$|: '); $|=0; for (1..10) { print(--$|, ' '); } print("\n");
print('$|++: '); $|=0; for (1..10) { print($|++, ' '); } print("\n");
print('++$|: '); $|=0; for (1..10) { print(++$|, ' '); } print("\n");

##</code><code>##

$|--: 0 1 0 1 0 1 0 1 0 1
--$|: 1 0 1 0 1 0 1 0 1 0
$|++: 0 1 1 1 1 1 1 1 1 1
++$|: 1 1 1 1 1 1 1 1 1 1

##</code><code>##

$,=", ";
$\="\n";
@list = qw( a b c d );

$| = 0;
print grep --$|,  @list;  # a, c

$t = 0;
print grep $t^=1, @list;  # a, c

##</code><code>##

$,=", ";
$\="\n";
@list = qw( a b c d e f );

$n = 3;
$t = $n-1;
print grep !($t=($t+1)%$n), @list;  # a, d