It's true. Yes you can get O(1) for user-defined types and O(N) for built-in types (of which Scheme has at least a dozen), but you can't get O(1) for all types,

It's true. Yes you can get O(1) for user-defined types and O(N) for built-in types (of which Scheme has at least a dozen), but you can't get O(1) for all types, as with first-class type tags.