Actions

Actions are named domain transitions you submit from app code.

Define actions in MEL. In TypeScript, call them through app.action.*.

Define an Action

domain TodoApp {
  type Todo = {
    id: string,
    title: string,
    completed: boolean
  }

  state {
    todos: Array<Todo> = []
  }

  action addTodo(title: string)
    dispatchable when trim(title) != "" {
    onceIntent {
      patch todos = append(todos, {
        id: $runtime.random.uuid,
        title: trim(title),
        completed: false
      })
    }
  }
}

Submit an Action

const result = await app.action.addTodo.submit("Learn actions");

if (result.ok && result.status === "settled" && result.outcome.kind === "ok") {
  console.log(result.after.state.todos);
}

submit() resolves with a runtime result. Read the returned after Snapshot, or call app.snapshot(), to see the visible state after the action settles.

Input Shape

The public argument shape follows the action declaration. A scalar parameter stays positional:

await app.action.addTodo.submit("Learn actions");

If the action declares a single object-shaped input, submit that object directly:

await app.action.configure.submit({ retries: 3, label: "daily" });

submit() does not wrap scalar inputs into { title }, and object-shaped inputs are not wrapped again into { input }.

Common Mistake

Do not dispatch raw string action names as your app-facing contract. Prefer app.action.someAction.submit(input).

Why The Keyword Is onceIntent

You will see the word "intent" in MEL keywords and lower-level API docs. In app code, you normally do not construct one yourself. Start with action handles, then read the Intent concept when you are building runtime tooling.

Next

Keep later UI state in sync with Subscriptions, then learn when actions should appear with Availability.