Persistent collections?

Afaik good implementations of Finger trees and RRB vectors compare reasonably well to javascript lists, but perform much better at operations where using mutable arrays leads to O(n^2) behaviour, especially for reactive code that compares a value to the old one to detect change.

Is there a good rescript implementation of persistent data structures with rescript providing strong typing? I am sort of surprised that Belt seems to have gone for immutable-but-not-persistent, given that it also does treeshaking, since that creates a misconception that immutability provides no performance benefits

Belt’s Map and Set types use AVL trees which are persistent. Is that what you’re looking for?

open Belt.Set.String
let s1 = empty->add("x")->add("y")->add("z")
let s2 = s1->add("a")
let s3 = s1->add("b")

In this example, the “y” and “z” parts of the set are persistent across all three structures. You can verify that by debugging the JS output.

Here persistent vector and WIP finger-tree based queue implementation

cc @namenu