makeSink > makeActionSink and makeEventSink, updates ToDo sample.

kotlin/samples/dungeon/common/src/main/java/com/squareup/sample/dungeon/PlayerWorkflow.kt

@@ -67,7 +67,7 @@ class PlayerWorkflow(
     state: Movement,
     context: RenderContext<Movement, Nothing>
   ): Rendering {
-    val sink = context.makeSink<Action>()
+    val sink = context.makeActionSink<Action>()
 
     return Rendering(
         actorRendering = ActorRendering(avatar = avatar, movement = state),

kotlin/samples/hello-workflow-fragment/src/main/java/com/squareup/sample/helloworkflowfragment/HelloWorkflow.kt

@@ -53,7 +53,7 @@ object HelloWorkflow : StatefulWorkflow<Unit, State, Nothing, Rendering>() {
     state: State,
     context: RenderContext<State, Nothing>
   ): Rendering {
-    val sink = context.makeSink<WorkflowAction<State, Nothing>>()
+    val sink = context.makeActionSink<WorkflowAction<State, Nothing>>()
     return Rendering(
         message = state.name,
         onClick = { sink.send(enterState(state.theOtherState())) }

kotlin/samples/hello-workflow/src/main/java/com/squareup/sample/helloworkflow/HelloWorkflow.kt

@@ -53,7 +53,7 @@ object HelloWorkflow : StatefulWorkflow<Unit, State, Nothing, Rendering>() {
     state: State,
     context: RenderContext<State, Nothing>
   ): Rendering {
-    val sink = context.makeSink<WorkflowAction<State, Nothing>>()
+    val sink = context.makeActionSink<WorkflowAction<State, Nothing>>()
     return Rendering(
         message = state.name,
         onClick = { sink.send(enterState(state.theOtherState())) }

kotlin/samples/tictactoe/common/src/main/java/com/squareup/sample/authworkflow/AuthWorkflow.kt

@@ -155,7 +155,7 @@ class RealAuthWorkflow(private val authService: AuthService) : AuthWorkflow,
     context: RenderContext<AuthState, AuthResult>
   ): BackStackScreen<*> {
 
-    val sink = context.makeSink<Action>()
+    val sink = context.makeActionSink<Action>()
 
     return when (state) {
       is LoginPrompt -> {

kotlin/samples/tictactoe/common/src/main/java/com/squareup/sample/gameworkflow/RunGameWorkflow.kt

@@ -183,7 +183,7 @@ class RealRunGameWorkflow(
     state: RunGameState,
     context: RenderContext<RunGameState, RunGameResult>
   ): RunGameScreen {
-    val sink = context.makeSink<Action>()
+    val sink = context.makeActionSink<Action>()
 
     return when (state) {
       is NewGame -> {

kotlin/samples/tictactoe/common/src/main/java/com/squareup/sample/gameworkflow/TakeTurnsWorkflow.kt

@@ -86,7 +86,7 @@ class RealTakeTurnsWorkflow : TakeTurnsWorkflow,
     state: Turn,
     context: RenderContext<Turn, CompletedGame>
   ): GamePlayScreen {
-    val sink = context.makeSink<Action>()
+    val sink = context.makeActionSink<Action>()
 
     return GamePlayScreen(
         playerInfo = input.playerInfo,

kotlin/samples/todo-android/app/src/main/java/com/squareup/sample/mainactivity/TodoEditorLayoutRunner.kt

@@ -15,16 +15,10 @@
  */
 package com.squareup.sample.mainactivity
 
-import androidx.appcompat.widget.Toolbar
 import android.view.View
 import android.widget.EditText
+import androidx.appcompat.widget.Toolbar
 import com.squareup.sample.todo.R
-import com.squareup.sample.todo.TodoEvent
-import com.squareup.sample.todo.TodoEvent.DeleteClicked
-import com.squareup.sample.todo.TodoEvent.DoneClicked
-import com.squareup.sample.todo.TodoEvent.GoBackClicked
-import com.squareup.sample.todo.TodoEvent.TextChanged
-import com.squareup.sample.todo.TodoEvent.TitleChanged
 import com.squareup.sample.todo.TodoRendering
 import com.squareup.workflow.ui.ExperimentalWorkflowUi
 import com.squareup.workflow.ui.LayoutRunner
@@ -57,27 +51,19 @@ internal class TodoEditorLayoutRunner(private val view: View) : LayoutRunner<Tod
     titleText.text.replace(0, titleText.text.length, rendering.list.title)
     itemContainer.setRows(rendering.list.rows.map { Pair(it.done, it.text) })
 
-    // Make event handling idempotent.
-    var eventFired = false
-    fun onEvent(event: TodoEvent) {
-      if (eventFired) return
-      eventFired = true
-      rendering.onEvent(event)
-    }
-
-    toolbar.setNavigationOnClickListener { onEvent(GoBackClicked) }
-    view.setBackHandler { onEvent(GoBackClicked) }
+    toolbar.setNavigationOnClickListener { rendering.onGoBackClicked() }
+    view.setBackHandler { rendering.onGoBackClicked() }
 
-    titleText.setTextChangedListener { onEvent(TitleChanged(it)) }
+    titleText.setTextChangedListener { rendering.onTitleChanged(it) }
 
     itemContainer.onDoneClickedListener = { index ->
-      onEvent(DoneClicked(index))
+      rendering.onDoneClicked(index)
     }
     itemContainer.onTextChangedListener = { index, text ->
-      onEvent(TextChanged(index, text))
+      rendering.onTextChanged(index, text)
     }
     itemContainer.onDeleteClickedListener = { index ->
-      onEvent(DeleteClicked(index))
+      rendering.onDeleteClicked(index)
     }
   }
 

kotlin/samples/todo-android/common/src/main/java/com/squareup/sample/todo/TodoEditorWorkflow.kt

@@ -15,16 +15,18 @@
  */
 package com.squareup.sample.todo
 
+import com.squareup.sample.todo.TodoAction.GoBackClicked
+import com.squareup.sample.todo.TodoAction.ListAction.DeleteClicked
+import com.squareup.sample.todo.TodoAction.ListAction.DoneClicked
+import com.squareup.sample.todo.TodoAction.ListAction.TextChanged
+import com.squareup.sample.todo.TodoAction.ListAction.TitleChanged
 import com.squareup.sample.todo.TodoEditorOutput.Done
 import com.squareup.sample.todo.TodoEditorOutput.ListUpdated
-import com.squareup.sample.todo.TodoEvent.DeleteClicked
-import com.squareup.sample.todo.TodoEvent.DoneClicked
-import com.squareup.sample.todo.TodoEvent.GoBackClicked
-import com.squareup.sample.todo.TodoEvent.TextChanged
-import com.squareup.sample.todo.TodoEvent.TitleChanged
 import com.squareup.workflow.RenderContext
+import com.squareup.workflow.Sink
 import com.squareup.workflow.StatelessWorkflow
-import com.squareup.workflow.WorkflowAction.Companion.emitOutput
+import com.squareup.workflow.WorkflowAction
+import com.squareup.workflow.WorkflowAction.Mutator
 
 data class TodoList(
   val title: String,
@@ -36,50 +38,84 @@ data class TodoRow(
   val done: Boolean = false
 )
 
-data class TodoRendering(
+sealed class TodoAction : WorkflowAction<Nothing, TodoEditorOutput> {
+  object GoBackClicked : TodoAction()
+
+  sealed class ListAction : TodoAction() {
+    abstract val list: TodoList
+
+    class TitleChanged(
+      override val list: TodoList,
+      val newTitle: String
+    ) : ListAction()
+
+    class DoneClicked(
+      override val list: TodoList,
+      val index: Int
+    ) : ListAction()
+
+    class TextChanged(
+      override val list: TodoList,
+      val index: Int,
+      val newText: String
+    ) : ListAction()
+
+    class DeleteClicked(
+      override val list: TodoList,
+      val index: Int
+    ) : ListAction()
+  }
+
+  override fun Mutator<Nothing>.apply(): TodoEditorOutput {
+    return when (this@TodoAction) {
+      is GoBackClicked -> Done
+      is TitleChanged -> ListUpdated(list.copy(title = newTitle))
+      is DoneClicked -> ListUpdated(list.updateRow(index) { copy(done = !done) })
+      is TextChanged -> ListUpdated(list.updateRow(index) { copy(text = newText) })
+      is DeleteClicked -> ListUpdated(list.removeRow(index))
+    }
+  }
+}
+
+class TodoRendering(
   val list: TodoList,
-  val onEvent: (TodoEvent) -> Unit
+  val onTitleChanged: (title: String) -> Unit,
+  val onDoneClicked: (index: Int) -> Unit,
+  val onTextChanged: (index: Int, text: String) -> Unit,
+  val onDeleteClicked: (index: Int) -> Unit,
+  val onGoBackClicked: () -> Unit
 )
 
 sealed class TodoEditorOutput {
   data class ListUpdated(val newList: TodoList) : TodoEditorOutput()
   object Done : TodoEditorOutput()
 }
 
-sealed class TodoEvent {
-  data class TitleChanged(val title: String) : TodoEvent()
-  data class DoneClicked(val index: Int) : TodoEvent()
-  data class TextChanged(
-    val index: Int,
-    val text: String
-  ) : TodoEvent()
-
-  data class DeleteClicked(val index: Int) : TodoEvent()
-  object GoBackClicked : TodoEvent()
-}
-
 class TodoEditorWorkflow : StatelessWorkflow<TodoList, TodoEditorOutput, TodoRendering>() {
 
   override fun render(
     input: TodoList,
     context: RenderContext<Nothing, TodoEditorOutput>
   ): TodoRendering {
+    val rawSink = context.makeActionSink<TodoAction>()
+
+    // Make event handling idempotent until https://github.com/square/workflow/issues/541 is fixed.
+    var eventFired = false
+    val sink = object : Sink<TodoAction> {
+      override fun send(value: TodoAction) {
+        if (eventFired) return
+        eventFired = true
+        rawSink.send(value)
+      }
+    }
+
     return TodoRendering(
-        list = input.copy(rows = input.rows + TodoRow("")),
-        onEvent = context.onEvent {
-          println("got event: $it")
-          when (it) {
-            is GoBackClicked -> emitOutput(Done)
-            is TitleChanged -> emitOutput(ListUpdated(input.copy(title = it.title)))
-            is DoneClicked -> emitOutput(ListUpdated(input.updateRow(it.index) {
-              copy(done = !done)
-            }))
-            is TextChanged -> emitOutput(ListUpdated(input.updateRow(it.index) {
-              copy(text = it.text)
-            }))
-            is DeleteClicked -> emitOutput(ListUpdated(input.removeRow(it.index)))
-          }
-        }
+        input.copy(rows = input.rows + TodoRow("")),
+        onTitleChanged = { sink.send(TitleChanged(input, it)) },
+        onDoneClicked = { sink.send(DoneClicked(input, it)) },
+        onTextChanged = { index, newText -> sink.send(TextChanged(input, index, newText)) },
+        onDeleteClicked = { sink.send(DeleteClicked(input, it)) },
+        onGoBackClicked = { sink.send(GoBackClicked) }
     )
   }
 }

kotlin/samples/todo-android/common/src/main/java/com/squareup/sample/todo/TodoListsWorkflow.kt

@@ -16,8 +16,9 @@
 package com.squareup.sample.todo
 
 import com.squareup.workflow.RenderContext
+import com.squareup.workflow.Sink
 import com.squareup.workflow.StatelessWorkflow
-import com.squareup.workflow.WorkflowAction.Companion.emitOutput
+import com.squareup.workflow.makeEventSink
 
 data class TodoListsRendering(
   val lists: List<TodoList>,
@@ -29,8 +30,9 @@ class TodoListsWorkflow : StatelessWorkflow<List<TodoList>, Int, TodoListsRender
     input: List<TodoList>,
     context: RenderContext<Nothing, Int>
   ): TodoListsRendering {
-    return TodoListsRendering(input, context.onEvent { row ->
-      emitOutput(row)
-    })
+    // A sink that emits the given index as the result of this workflow.
+    val sink: Sink<Int> = context.makeEventSink { index: Int -> index }
+
+    return TodoListsRendering(lists = input, onRowClicked = sink::send)
   }
 }

kotlin/workflow-core/src/main/java/com/squareup/workflow/RenderContext.kt

@@ -21,14 +21,15 @@ import com.squareup.workflow.Worker.OutputOrFinished
 import com.squareup.workflow.Worker.OutputOrFinished.Finished
 import com.squareup.workflow.Worker.OutputOrFinished.Output
 import com.squareup.workflow.WorkflowAction.Companion.noAction
+import com.squareup.workflow.WorkflowAction.Mutator
 
 /**
  * Facilities for a [Workflow] to interact with other [Workflow]s and the outside world from inside
  * a `render` function.
  *
  * ## Handling Events
  *
- * See [onEvent].
+ * See [makeActionSink].
  *
  * ## Performing Asynchronous Work
  *
@@ -40,12 +41,20 @@ import com.squareup.workflow.WorkflowAction.Companion.noAction
  */
 interface RenderContext<StateT, in OutputT : Any> {
 
-  @Deprecated("Use makeSink.")
+  @Deprecated("Use makeActionSink.")
   fun <EventT : Any> onEvent(
     handler: (EventT) -> WorkflowAction<StateT, OutputT>
   ): (EventT) -> Unit
 
-  fun <A : WorkflowAction<StateT, OutputT>> makeSink(): Sink<A>
+  /**
+   * Creates a sink that will a single [WorkflowAction] of the given type.
+   * Invokes that action by calling [WorkflowAction.apply] to update the current
+   * state, and optionally emit the returned output value if it is non-null.
+   *
+   * Note that only a single action can be processed the sink (or sinks) created
+   * during a `render` call. Redundant calls to [Sink.send] will
+   */
+  fun <A : WorkflowAction<StateT, OutputT>> makeActionSink(): Sink<A>
 
   /**
    * Ensures [child] is running as a child of this workflow, and returns the result of its
@@ -96,10 +105,10 @@ fun <StateT, OutputT : Any, ChildOutputT : Any, ChildRenderingT>
 // Intellij refuses to format this parameter list correctly because of the weird line break,
 // and detekt will complain about it.
 // @formatter:off
-      child: Workflow<Unit, ChildOutputT, ChildRenderingT>,
-      key: String = "",
-      handler: (ChildOutputT) -> WorkflowAction<StateT, OutputT>
-    ): ChildRenderingT = renderChild(child, Unit, key, handler)
+  child: Workflow<Unit, ChildOutputT, ChildRenderingT>,
+  key: String = "",
+  handler: (ChildOutputT) -> WorkflowAction<StateT, OutputT>
+): ChildRenderingT = renderChild(child, Unit, key, handler)
 // @formatter:on
 
 /**
@@ -111,10 +120,10 @@ fun <InputT, StateT, OutputT : Any, ChildRenderingT>
 // Intellij refuses to format this parameter list correctly because of the weird line break,
 // and detekt will complain about it.
 // @formatter:off
-      child: Workflow<InputT, Nothing, ChildRenderingT>,
-      input: InputT,
-      key: String = ""
-    ): ChildRenderingT = renderChild(child, input, key) { noAction() }
+  child: Workflow<InputT, Nothing, ChildRenderingT>,
+  input: InputT,
+  key: String = ""
+): ChildRenderingT = renderChild(child, input, key) { noAction() }
 // @formatter:on
 
 /**
@@ -126,9 +135,9 @@ fun <StateT, OutputT : Any, ChildRenderingT>
 // Intellij refuses to format this parameter list correctly because of the weird line break,
 // and detekt will complain about it.
 // @formatter:off
-      child: Workflow<Unit, Nothing, ChildRenderingT>,
-      key: String = ""
-    ): ChildRenderingT = renderChild(child, Unit, key) { noAction() }
+  child: Workflow<Unit, Nothing, ChildRenderingT>,
+  key: String = ""
+): ChildRenderingT = renderChild(child, Unit, key) { noAction() }
 // @formatter:on
 
 /**
@@ -166,3 +175,17 @@ fun <StateT, OutputT : Any> RenderContext<StateT, OutputT>.runningWorker(
     throw AssertionError("Worker<Nothing> emitted $it")
   }
 }
+
+/**
+ * Alternative to [RenderContext.makeActionSink] that allows externally defined
+ * event types to be mapped to anonymous [WorkflowAction]s.
+ */
+fun <EventT, StateT, OutputT : Any> RenderContext<StateT, OutputT>.makeEventSink(
+  block: Mutator<StateT>.(EventT) -> OutputT
+): Sink<EventT> {
+  val actionSink = makeActionSink<WorkflowAction<StateT, OutputT>>()
+
+  return actionSink.contraMap { event ->
+    WorkflowAction { block.invoke(this, event) }
+  }
+}

kotlin/workflow-core/src/main/java/com/squareup/workflow/Sink.kt

@@ -2,7 +2,7 @@ package com.squareup.workflow
 
 /**
  * An object that receives values (commonly events or [WorkflowAction]).
- * Use [RenderContext.makeSink] to create instances.
+ * Use [RenderContext.makeActionSink] to create instances.
  */
 interface Sink<T> {
   fun send(value: T)

kotlin/workflow-core/src/main/java/com/squareup/workflow/WorkflowAction.kt

@@ -24,6 +24,11 @@ import com.squareup.workflow.WorkflowAction.Mutator
 interface WorkflowAction<StateT, out OutputT : Any> {
   class Mutator<S>(var state: S)
 
+  /**
+   * Called with the current state of a workflow, allowing the state to be updated.
+   *
+   * @return an output value for the workflow to emit, or null to emit nothing.
+   */
   fun Mutator<StateT>.apply(): OutputT?
 
   companion object {

kotlin/workflow-runtime/src/main/java/com/squareup/workflow/internal/RealRenderContext.kt

@@ -70,7 +70,7 @@ class RealRenderContext<StateT, OutputT : Any>(
     }
   }
 
-  override fun <A : WorkflowAction<StateT, OutputT>> makeSink(): Sink<A> {
+  override fun <A : WorkflowAction<StateT, OutputT>> makeActionSink(): Sink<A> {
     checkNotFrozen()
 
     return object : Sink<A> {