Yield
-----
<?php

function gen()
{
    yield;
    yield $a;
    yield $a => $b;
    $a = yield;
    $a = yield $b;
    $a = yield $b => $c;
    yield from $a;
    $a = yield from $b;
    (yield $a) + $b;
    (yield from $a) + $b;
    [yield $a => $b];
    [(yield $a) => $b];
    [$a + (yield $b) => $c];
    yield yield $a => $b;
    yield (yield $a) => $b;
    match ($x) {
        yield $a, (yield $b) => $c,
    };
    yield -$a;
    (yield) - $a;
    yield * $a;
}
-----
function gen()
{
    yield;
    yield $a;
    yield $a => $b;
    $a = yield;
    $a = yield $b;
    $a = yield $b => $c;
    yield from $a;
    $a = yield from $b;
    (yield $a) + $b;
    (yield from $a) + $b;
    [yield $a => $b];
    [(yield $a) => $b];
    [$a + (yield $b) => $c];
    yield yield $a => $b;
    yield (yield $a) => $b;
    match ($x) {
        yield $a, (yield $b) => $c,
    };
    yield -$a;
    (yield) - $a;
    (yield) * $a;
}
-----
<?php

function gen()
{
    yield;
    yield $a;
    yield $a => $b;
    $a = yield;
    $a = yield $b;
    $a = yield $b => $c;
    yield from $a;
    $a = yield from $b;
    (yield $a) + $b;
    (yield from $a) + $b;
    [yield $a => $b];
    [(yield $a) => $b];
    [$a + (yield $b) => $c];
    yield yield $a => $b;
    yield (yield $a) => $b;
    match ($x) {
        yield $a, (yield $b) => $c,
    };
    yield -$a;
    (yield) - $a;
    yield * $a;
}
-----
!!version=5.6,parserVersion=8.0
function gen()
{
    yield;
    (yield $a);
    (yield $a => $b);
    $a = yield;
    $a = (yield $b);
    $a = (yield $b => $c);
    yield from $a;
    $a = yield from $b;
    (yield $a) + $b;
    (yield from $a) + $b;
    [(yield $a => $b)];
    [(yield $a) => $b];
    [$a + (yield $b) => $c];
    (yield (yield $a => $b));
    (yield (yield $a) => $b);
    match ($x) {
        (yield $a), (yield $b) => $c,
    };
    (yield -$a);
    (yield) - $a;
    (yield) * $a;
}