Strategy

Verifies if I can be accepted.

If this yields to true, then the pubsub can accept this element, and interpreter is free to invoke publish. If this yields to false, then interpreter holds the publisher, until there is at least one get (either successsful or not) in which case this is consulted again.

Yields to true if there are no elements to get.

Gets O, selected by selector.

Yields to None, if subscriber cannot be satisfied, causing the subscriber to hold, until next successful publish Yields to Some((s,o)) if the subscriber may be satisfied.

Initial state of this strategy. *

Publishes I. This must always succeed.

Interpreter must only invoke this when accepts yields to true.

Consulted by interpreter to subscribe the given selector. A subscriptions manages context/state across multiple get requests. Yields to false if the subscription cannot be satisfied.

Transforms selector to selector of this state by applying the f to Sel2 and state of this strategy. *

When strategy supports long-term subscriptions, this is used by interpreter to cancel a previous subscription, indicating the subscriber is no longer interested in getting more data.