C:\>perl -MO=Deparse -we "sub DEBUG{0}print 'this' if DEBUG;"
sub DEBUG {
    0;
}
print 'this' if DEBUG ;
-e syntax OK

C:\>perl -MO=Deparse -we "sub DEBUG(){0}print 'this' if DEBUG;"
sub DEBUG () {
    0;
}
'???';
-e syntax OK