readonly function
-----
<?php
function readonly() {}
readonly();
-----
array(
    0: Stmt_Function(
        attrGroups: array(
        )
        byRef: false
        name: Identifier(
            name: readonly
        )
        params: array(
        )
        returnType: null
        stmts: array(
        )
    )
    1: Stmt_Expression(
        expr: Expr_FuncCall(
            name: Name(
                parts: array(
                    0: readonly
                )
            )
            args: array(
            )
        )
    )
)