seamless doesn't implement the "persistent" part of immutable persistent data structures. The persistent part means you can create a cheap modification of the data structure, with structural sharing between "copies".
I.E. if I have {a:{aa:"1"},b:"cc"} and I change b, then {aa:"1"} will not be deep copied.
Are you talking about something like keeping a reference to the parent and sending lookups up the chain (with a prototype or some such?)
> Persistent data structures are different, as their performance improvements are passive. Although seamless-immutable does not (and cannot, while maintaining its backwards compatibility with vanilla JS collections) use things like VLists under the hood, its cloning functions—such as merge—only bother to make shallow copies, as shallow and deep copies of immutable values are equivalent. In practice, this simple passive optimization has been sufficient; we have yet to encounter a performance problem that Bagwell-style persistent data structures would have solved.
from: http://tech.noredink.com/post/107617838018/switching-from-im...
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This is also awesome for parallelization where you want to share data but don't need synchronization!