gust-stdlib 0.4.1

Standard library of reusable Gust state machines (circuit breaker, retry, saga, rate limiter, and more)
Documentation 
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// Token-bucket admission control.
//
// Not keyed: this limiter governs a single bucket. It previously declared a
// type parameter `K` that no state, effect, or handler ever referenced, which
// generated Rust that did not compile (E0392). Per-key limiting is a feature
// change — it needs the key in the state, e.g. `state Available(key: K, ...)`
// — not a bare parameter on the header.
machine RateLimiter {
    state Available(tokens: i64, max_tokens: i64)
    state Exhausted(retry_after_ms: i64, max_tokens: i64)

    transition acquire: Available -> Available | Exhausted
    transition refill: Exhausted -> Available

    effect now_ms() -> i64

    on acquire() {
        if tokens > 0 {
            goto Available(tokens - 1, max_tokens);
        } else {
            goto Exhausted(perform now_ms(), max_tokens);
        }
    }

    on refill() {
        goto Available(max_tokens, max_tokens);
    }
}