Typed events

This example sends progress notifications while an asynchronous command runs. It demonstrates the separate roles of a command response and an event subscription when displaying ongoing backend work.

40_event_broadcast · Source files: main.mbt, app.html

Behavior

Starting the ticker produces tick events and a done event. The command also returns its collected result. The run_id distinguishes runs.

Implementation

Excerpt from the entry point; use the source link above for the complete context.

async fn run_ticker(
  context : @proton.CommandContext,
  payload : StartPayload,
) -> TickerResult {
  let count = clamp(payload.count, 1, 20)
  let interval_ms = clamp(payload.interval_ms, 100, 2000)
  let ticks : Array[TickEvent] = []
  for index in 1..<=count {
    @async.sleep(interval_ms)
    let tick = TickEvent::{
      run_id: payload.run_id,
      index,
      total: count,
      remaining: count - index,
    }
    ticks.push(tick)
    context.emit(tick_event, tick)
  }
  let done = DoneEvent::{ run_id: payload.run_id, total: count, }
  context.emit(done_event, done)
  TickerResult::{ ticks, done, }
}

A typed extension binds start to run_ticker. The handler awaits between ticks and emits tick/done notifications before returning a final TickerResult. Progress events and the command result have separate roles: a displayed tick is not completion of the command.

The count and interval are clamped by the backend. Reuse the request id in your UI to distinguish overlapping runs, close subscriptions with their owner, and handle request cancellation. Despite the historical directory name, this is not a durable broadcast log.

Run

After completing source checkout and runtime setup, run from the repository root:

moon -C examples run 40_event_broadcast --target native

Limits and interpretation

Events and command responses serve different purposes. Register listeners before starting a run; an event is not a durable history or an acknowledgement.