Kotlin Translations for Event-Compose, Monad, and Prototype Examples

Kotlin/event-compose.kt

@@ -0,0 +1,45 @@
+import java.util.*
+
+class Point(x: Int, y: Int) {
+    private var x: Int = x
+    private var y: Int = y
+    val emitter = EventEmitter()
+
+    init {
+        emitter.on("move") { event ->
+            val map = event as Map<*, *>
+            this.x += (map["x"] as Int)
+            this.y += (map["y"] as Int)
+        }
+
+        emitter.on("clone") { callback ->
+            val point = Point(this.x, this.y)
+            (callback as (Point) -> Unit)(point)
+        }
+
+        emitter.on("toString") { callback ->
+            (callback as (String) -> Unit)("(${this.x}, ${this.y})")
+        }
+    }
+}
+
+class EventEmitter {
+    private val listeners = mutableMapOf<String, MutableList<(Any) -> Unit>>()
+
+    fun on(event: String, listener: (Any) -> Unit) {
+        listeners.computeIfAbsent(event) { mutableListOf() }.add(listener)
+    }
+
+    fun emit(event: String, arg: Any) {
+        listeners[event]?.forEach { it(arg) }
+    }
+}
+
+// Usage
+fun main() {
+    val p1 = Point(10, 20)
+    p1.emitter.emit("toString", { message: String -> println(message) })
+    p1.emitter.emit("clone") { c1: Point ->
+        c1.emitter.emit("toString", { message: String -> println(message) })
+        c1.emitter.emit("move", mapOf("x" to -5, "y" to 10))
+        c1.emitter.emit("toString", { message: String -> println(message) })

Kotlin/monad.kt

@@ -0,0 +1,46 @@
+data class Point(val x: Int, val y: Int)
+
+class Monad<T>(private val value: T) {
+
+    companion object {
+        fun <T> of(value: T): Monad<T> {
+            return Monad(value)
+        }
+    }
+
+    fun <R> map(fn: (T) -> R): Monad<R> {
+        val valueCopy = deepCopy(value)
+        return of(fn(valueCopy))
+    }
+
+    fun <R> chain(fn: (T) -> Monad<R>): Monad<R> {
+        val valueCopy = deepCopy(value)
+        return fn(valueCopy)
+    }
+
+    fun ap(container: Monad<Point>): Monad<Point> {
+        val fn = value as (Point) -> Point
+        return container.map(fn)
+    }
+
+    private fun <T> deepCopy(obj: T): T {
+        return when (obj) {
+            is Point -> Point(obj.x, obj.y) as T
+            else -> obj
+        }
+    }
+}
+
+val move: (Map<String, Int>) -> (Point) -> Point = { d -> { p -> Point(p.x + d["x"]!!, p.y + d["y"]!!) } }
+val clone: (Point) -> Point = { p -> Point(p.x, p.y) }
+val toString: (Point) -> Monad<String> = { p -> Monad.of("(${p.x}, ${p.y})") }
+
+// Usage
+fun main() {
+    val p1 = Monad.of(Point(10, 20))
+    p1.chain(toString).map { println(it) }
+    val c0 = p1.map(clone)
+    val t1 = Monad.of(move(mapOf("x" to -5, "y" to 10)))
+    val c1 = t1.ap(c0)
+    c1.chain(toString).map { println(it) }
+}

Kotlin/prototype.kt

@@ -0,0 +1,24 @@
+class Point(var x: Int, var y: Int) {
+
+    fun clone(): Point {
+        return Point(x, y)
+    }
+
+    fun move(x: Int, y: Int) {
+        this.x += x
+        this.y += y
+    }
+
+    override fun toString(): String {
+        return "(${x}, ${y})"
+    }
+}
+
+// Usage
+fun main() {
+    val p1 = Point(10, 20)
+    println(p1.toString())
+    val c1 = p1.clone()
+    c1.move(-5, 10)
+    println(c1.toString())
+}