constellation/core

Deterministic protocol transitions for demand-driven stages.

Types

StageState

opaque </>

Protocol state owned by a stage.

Its representation is hidden so subscriptions, demand, dispatch order, and buffered events can only change through validated commands.

pub opaque type StageState(event)

Values

buffered_events

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pub fn buffered_events(state: StageState(event)) -> List(event)

Returns buffered events in FIFO order for inspection and testing.

is_cancelled

</>

pub fn is_cancelled(
  state: StageState(event),
  id: subscription_id.SubscriptionId,
) -> Bool

Reports whether an ID belongs to a subscription cancelled in this stage.

new

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pub fn new() -> StageState(event)

Creates an empty stage using demand-based round-robin dispatching.

new_with_strategy

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pub fn new_with_strategy(
  strategy: dispatcher.Strategy(event),
) -> StageState(event)

Creates an empty stage with the supplied dispatch strategy.

subscription

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pub fn subscription(
  state: StageState(event),
  id: subscription_id.SubscriptionId,
) -> Result(subscription.Subscription, stage_error.StageError)

Looks up an active subscription and distinguishes cancelled IDs from unknown IDs.

update

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pub fn update(
  state: StageState(event),
  command: command.Command(event),
) -> Result(
  #(StageState(event), List(effect.Effect(event))),
  stage_error.StageError,
)

Applies one protocol command and returns the new state plus runtime effects.