use strict;
use warnings;

use Data::Dumper;

sub a{
    return(undef, undef);
}

my($x, $y);
if(($x, $y) = a() ){
    print "OK1\n";
}

if((undef, undef) = a() ){
    print "OK2\n";
}

if(a()){
    print "OK3\n";
}

if(undef, undef){
    print "OK4\n";
}

##</code><code>##

OK1
OK2