$ perl -MO=Deparse -e 'sub ONE { 1 } if (ONE) { print ONE if ONE }'
sub ONE {
    1;
}
if (ONE) {
    print ONE() if ONE;
}
-e syntax OK

$ perl -MO=Deparse -e 'sub ONE () { 1 } if (ONE) { print ONE if ONE }'
sub ONE () {
    1;
}
do {
    print 1
};
-e syntax OK