Cycle giving baby steps into Kotlin

app.kt

import kotlin.browser.document
import kotlin.browser.window

// Type definitions
native("Cycle")
val Cycle : dynamic = noImpl

native("Cycle.h")
fun h(tagName: String) : VTree = noImpl

native("Cycle.h")
fun h(tagName: String, children: Array<VTree>) : VTree = noImpl

native("Cycle.h")
fun h(tagName: String, content: String) : VTree = noImpl

native("Cycle.makeDOMDriver")
fun makeDOMDriver(container: String): () -> Unit = noImpl

interface Observable {
    fun subscribe()
    fun map(fn: (input: dynamic) -> dynamic): Observable
    fun startWith(value: dynamic): Observable
}

interface VTree {
    val properties : dynamic
}

interface QueryableObservableCollection {
    fun get(vararg params: String): Observable
}

interface DriverResponseCollection {
    val DOM : QueryableObservableCollection
}

// Cycle app
fun app(drivers: dynamic): dynamic {
    return object {
        val DOM = drivers.DOM.get("input", "input")
            .map({ ev -> ev.target.value })
            .startWith("")
            .map({ name ->
                h("div", arrayOf(
                    h("input"), h("h2", "Hello $name")
                ))
            })
    }
}

// Kotlin main function initializing Cycle app
fun main(args: Array<String>) {
    window.addEventListener("load", {
        Cycle.run(::app, object {
            val DOM = makeDOMDriver("#app")
        })
    })
}

notes.md

Notes

• Kotlin's Type-Safe Builders are the most compelling feature useful for React, virtual-dom, Cycle, (think type-safe JSX) which TypeScript doesn't have as far as I know.
• Some minor guards and checks had to be added to Cycle.js core, because Kotlin inserts metadata noise in arbitrary objects.
• Not all types working, used dynamic when I didn't have patience/time to figure out the type system.
• Kotlin compiler does a bit too much pollution in JS which makes interop with JS libraries such as Cycle.js a bit harder.
• Kotlin feels good, but I haven't used TypeScript to compare them.
• I believe one can make a tool to automate the conversion of TypeScript definition files into Kotlin code with interfaces.
• No CommonJS support still, which sucks, but you can get things done by importing JS libraries with old-style <script>.

A lot of stuff has changed in the past year in the kotlin world. There have been a lot of additions to the JS/web support. I'm an Android developer, and have been following your work, specifically the MVI stuff. I've been applying principles to the android work that I do, and I'm curious to see how you apply kotlin principles to Cycle.js.

I think sealed types (algebraic data types) are a game changer for doing things like stream processing

CommonJS support

Typescript to kotlin converter

React app using kotlin