if ((my ($x, $y) = mysub ($args))[0]) {

##</code><code>##

my ($x, $y);
if ((($x, $y) = mysub ($args)) != 1 || !defined($x) || length($x) != 1 || $x != 0) {
   do stuff
}
else {  # Triggered on a single 0
   do other stuff
}