How to work with timers

Use a timer source when you need recurring or delayed external input. The timer itself is the outside-world boundary; everything downstream stays pure.

Example

type Unit -> Int -> Int
func countTicks = tick total =>
    total + 1

@source timer.every 1sec with {
    immediate: False,
    coalesce: True
}
signal tick : Signal Unit

signal elapsed = tick
 +|> 0 countTicks

signal label = elapsed
  |> "Ticks received: {.}"

value main =
    <Window title="Timer">
        <Label text={label} />
    </Window>

export main

Why this shape works

• timer.every creates a typed stream of events.
• +|> accumulates those events into state over time.
• coalesce: True avoids a backlog if the UI is briefly busy.
• Counting delivered ticks is not a precise elapsed-time measurement: coalescing can skip missed ticks. Use a monotonic clock when measuring elapsed time matters.

Common variations

• Use timer.after for one-shot delays.
• Feed a timer into refreshOn when polling an API.
• Keep timer logic small and move real state transitions into a named step function.