AlertPredicate

What it does

Consumer-side adapter that fires an AlertTick when a user-supplied predicate matches an analytic's emission. Composes with any typed row the callback delivers.

// Cargo.toml:
//   kairos = "0.1"
use kairos::{AlertPredicate, AlertTick, Client, GreeksRow};

let client = Client::connect(("me@example.com", "secret"))?;

// `AlertPredicate::new(closure)` constructs a value-typed predicate.
// Evaluate it against each row the `.on_event` callback delivers.
let predicate = AlertPredicate::new(|delta: &f64| delta.abs() > 0.5);

let sub = client
    .live()
    .greeks(["QQQ"])
    .on_event(move |row: &GreeksRow| {
        if predicate.evaluate(&row.delta) {
            let _ = AlertTick { value: row.delta };
        }
    })?;

// ... later ...
sub.unsubscribe();

API surface

Method	Returns
AlertPredicate::new(closure)	AlertPredicate<T>
predicate.evaluate(&T)	bool

The predicate is value-typed, not stream-typed. Composition is a consumer-side concern — drive the predicate inline in the .on_event callback or build an adapter type around it.

Replay parity

AlertPredicate is stateless — the underlying analytic's emission stream carries replay-parity by construction; the predicate is a pure function. Replay equivalence is preserved end-to-end.

Why a primitive

Cross-analytic alerting is a common downstream concern. The predicate adapter keeps the alerting vocabulary out of every individual analytic's spec and lets the consumer compose the same predicate shape against any output stream.