for my $idx (reverse 0 .. $#array) {
    my $item = $array[$idx];
    if (some_test($item)) {
        splice(@array, $idx, 1); # remove the element
    }
}

##</code><code>##

while (@work) {
    my $item = shift/pop @work;
    # Possibly push/unshift items onto @work
}