/* custom error: The linear value has already been used */
select Block(($parent)->{
        $list = Opaque([ToDynamicLinear(ToMutDict({"a":1},$parent))]);
        $a, $b = (Unwrap(ListHead($list)), Unwrap(ListLast($list)));
        return (FromMutDict(FromDynamicLinear($a)), FromMutDict(FromDynamicLinear($b)));
});