class TaggedValue;
class Tuple;
template <class T>
// TODO(ccrusius): Use absl::Hash specializations instead.
class TaggedValueHash;
using List = std::vector<TaggedValue>;
using ListPtr = std::shared_ptr<List>;
using Dict =
    absl::flat_hash_map<TaggedValue, TaggedValue, TaggedValueHash<TaggedValue>>;
using DictPtr = std::shared_ptr<Dict>;
using TuplePtr = std::shared_ptr<Tuple>;
using Func =