chore: write example code for reducer over optional state

Author: gyulavoros

composable-architecture/src/test/kotlin/composablearchitecture/sandbox/optional/Sandbox.kt

@@ -0,0 +1,64 @@
+package composablearchitecture.sandbox.optional
+
+import arrow.optics.Prism
+import arrow.optics.optics
+import composablearchitecture.Reducer
+import composablearchitecture.Store
+import composablearchitecture.withNoEffect
+import kotlinx.coroutines.flow.collect
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.test.TestCoroutineDispatcher
+
+@optics
+data class AppState(val text: String? = null) {
+    companion object
+}
+
+sealed class AppAction {
+    data class UpdateText(val to: String) : AppAction()
+}
+
+val optionalReducer = Reducer<String, AppAction, Unit> { _, action, _ ->
+    when (action) {
+        is AppAction.UpdateText -> action.to.withNoEffect()
+    }
+}.optional()
+
+val appReducer: Reducer<AppState, AppAction, Unit> = optionalReducer.pullback(
+    toLocalState = AppState.nullableText,
+    toLocalAction = Prism.id(),
+    toLocalEnvironment = { Unit }
+)
+
+fun main() {
+    runBlocking {
+        val testDispatcher = TestCoroutineDispatcher()
+
+        println("🎬 initial state is non-null")
+
+        var store = Store(
+            initialState = AppState(text = ""),
+            reducer = appReducer,
+            environment = Unit,
+            mainDispatcher = testDispatcher
+        )
+        var job = launch(testDispatcher) { store.states.collect { println(it) } }
+        store.send(AppAction.UpdateText("Update non-null state"))
+        job.cancel()
+
+        println("🎬 initial state is null")
+
+        store = Store(
+            initialState = AppState(text = null),
+            reducer = appReducer,
+            environment = Unit,
+            mainDispatcher = testDispatcher
+        )
+        job = launch(testDispatcher) { store.states.collect { println(it) } }
+        store.send(AppAction.UpdateText("Update null state"))
+        job.cancel()
+
+        println("✅")
+    }
+}