Generators (yield expression)
-----
<?php

function gen() {
    // statements
    yield;
    yield $value;
    yield $key => $value;

    // expressions
    $data = yield;
    $data = (yield $value);
    $data = (yield $key => $value);

    // yield in language constructs with their own parentheses
    if (yield $foo); elseif (yield $foo);
    if (yield $foo): elseif (yield $foo): endif;
    while (yield $foo);
    do {} while (yield $foo);
    switch (yield $foo) {}
    die(yield $foo);

    // yield in function calls
    func(yield $foo);
    $foo->func(yield $foo);
    new Foo(yield $foo);

    yield from $foo;
    yield from $foo and yield from $bar;
    yield from $foo + $bar;
}
-----
array(
    0: Stmt_Function(
        byRef: false
        name: gen
        params: array(
        )
        returnType: null
        stmts: array(
            0: Expr_Yield(
                key: null
                value: null
            )
            1: Expr_Yield(
                key: null
                value: Expr_Variable(
                    name: value
                )
            )
            2: Expr_Yield(
                key: Expr_Variable(
                    name: key
                )
                value: Expr_Variable(
                    name: value
                )
            )
            3: Expr_Assign(
                var: Expr_Variable(
                    name: data
                )
                expr: Expr_Yield(
                    key: null
                    value: null
                )
            )
            4: Expr_Assign(
                var: Expr_Variable(
                    name: data
                )
                expr: Expr_Yield(
                    key: null
                    value: Expr_Variable(
                        name: value
                    )
                )
            )
            5: Expr_Assign(
                var: Expr_Variable(
                    name: data
                )
                expr: Expr_Yield(
                    key: Expr_Variable(
                        name: key
                    )
                    value: Expr_Variable(
                        name: value
                    )
                )
            )
            6: Stmt_If(
                cond: Expr_Yield(
                    key: null
                    value: Expr_Variable(
                        name: foo
                    )
                )
                stmts: array(
                )
                elseifs: array(
                    0: Stmt_ElseIf(
                        cond: Expr_Yield(
                            key: null
                            value: Expr_Variable(
                                name: foo
                            )
                        )
                        stmts: array(
                        )
                    )
                )
                else: null
            )
            7: Stmt_If(
                cond: Expr_Yield(
                    key: null
                    value: Expr_Variable(
                        name: foo
                    )
                )
                stmts: array(
                )
                elseifs: array(
                    0: Stmt_ElseIf(
                        cond: Expr_Yield(
                            key: null
                            value: Expr_Variable(
                                name: foo
                            )
                        )
                        stmts: array(
                        )
                    )
                )
                else: null
            )
            8: Stmt_While(
                cond: Expr_Yield(
                    key: null
                    value: Expr_Variable(
                        name: foo
                    )
                )
                stmts: array(
                )
            )
            9: Stmt_Do(
                cond: Expr_Yield(
                    key: null
                    value: Expr_Variable(
                        name: foo
                    )
                )
                stmts: array(
                )
            )
            10: Stmt_Switch(
                cond: Expr_Yield(
                    key: null
                    value: Expr_Variable(
                        name: foo
                    )
                )
                cases: array(
                )
            )
            11: Expr_Exit(
                expr: Expr_Yield(
                    key: null
                    value: Expr_Variable(
                        name: foo
                    )
                )
            )
            12: Expr_FuncCall(
                name: Name(
                    parts: array(
                        0: func
                    )
                )
                args: array(
                    0: Arg(
                        value: Expr_Yield(
                            key: null
                            value: Expr_Variable(
                                name: foo
                            )
                        )
                        byRef: false
                        unpack: false
                    )
                )
            )
            13: Expr_MethodCall(
                var: Expr_Variable(
                    name: foo
                )
                name: func
                args: array(
                    0: Arg(
                        value: Expr_Yield(
                            key: null
                            value: Expr_Variable(
                                name: foo
                            )
                        )
                        byRef: false
                        unpack: false
                    )
                )
            )
            14: Expr_New(
                class: Name(
                    parts: array(
                        0: Foo
                    )
                )
                args: array(
                    0: Arg(
                        value: Expr_Yield(
                            key: null
                            value: Expr_Variable(
                                name: foo
                            )
                        )
                        byRef: false
                        unpack: false
                    )
                )
            )
            15: Expr_YieldFrom(
                expr: Expr_Variable(
                    name: foo
                )
            )
            16: Expr_BinaryOp_LogicalAnd(
                left: Expr_YieldFrom(
                    expr: Expr_Variable(
                        name: foo
                    )
                )
                right: Expr_YieldFrom(
                    expr: Expr_Variable(
                        name: bar
                    )
                )
            )
            17: Expr_YieldFrom(
                expr: Expr_BinaryOp_Plus(
                    left: Expr_Variable(
                        name: foo
                    )
                    right: Expr_Variable(
                        name: bar
                    )
                )
            )
        )
    )
)