Subscribing to Events

Subscribe statements appear in state notes and register listeners on the EventAdapter. When a matching event arrives on the EventBus, the adapter translates it into an Action and dispatches it to the FSM — regardless of which state the machine is currently in.

Syntax

subscribe/<EVENT_NAME> <ACTION_NAME>
subscribe/<EVENT_NAME> <ACTION_NAME> (<PAYLOAD_KEY_LIST>)
subscribe/<EVENT_NAME> <ACTION_NAME> (<PAYLOAD_KEY_LIST>) <= (<META_KEY_LIST>)

Part	Description
EVENT_NAME	Globally unique event identifier (see Events)
ACTION_NAME	Action to dispatch when the event fires
PAYLOAD_KEY_LIST	$key names exposed as action payload properties
<= (<META_KEY_LIST>)	Maps incoming event meta fields (by position) to payload keys

Examples

note right of Idle
  subscribe/userLoggedIn AUTHENTICATE
  subscribe/userLoggedIn AUTHENTICATE ($userId)
  subscribe/userLoggedIn AUTHENTICATE ($userId) <= ($id)
end note

Form	Dispatched payload	Meta field used
bare	{}	-
with payload	{ userId: meta.userId }	meta.userId (same name)
with meta mapping	{ userId: meta.id }	meta.id mapped to $userId

Multiple subscriptions in one note are allowed. Each fires independently.

Flow

Note: Subscription is not state-gated. The listener fires regardless of the FSM's current state.

Placement

subscribe statements may appear in any state's note. The note's host state does not affect when the listener fires — the placement is purely organizational.

See Events and Event Model.