This is a quick little project I've spent the past few days working on. This page lets you study and observe the functions from Swift Algorithms[0] in real time.
The HTML/CSS was generated using HyperSwift[1] and the DOM control/manipulation is done with SwiftWASM[2].
That is to say, this is very close to being written 100% in Swift.
[0] https://github.com/apple/swift-algorithms
[1] https://github.com/johngarrett/hyperSwift
[2] http://swiftwasm.org