workaround for &eval being an only-sub

eval.pl

proto eval(|$) {*};
multi sub eval($str) {
    $str.eval;
}
multi sub eval($str, :$lang! where 'perl5') {
    'dummy p5 return value';
}

say eval('2 + 2');
say eval('2 + 2', :lang<perl5>);