You can totally start learning and experimenting with SwiftUI in an Xcode playground. Just import PlaygroundSupport, and assign a UIHostingController as your live view:

import SwiftUI
import PlaygroundSupport

struct MyView: View {
    var body: some View {
        Text("Hello, world!")
    }
}

let vc = UIHostingController(rootView: MyView())
PlaygroundPage.current.liveView = vc