$ perl -MO=Deparse -e 'while (<>) {} while ( <ARGV> ) {} while ( $_ = <> ) {} while ( $x = <> ) {}'
while (defined($_ = <ARGV>)) {
    ();
}
while (defined($_ = <ARGV>)) {
    ();
}
while (defined($_ = <ARGV>)) {
    ();
}
while (defined($x = <ARGV>)) {
    ();
}
-e syntax OK