Guards and actions

JSON charts name their logic; Rust supplies it in a MachineLogic:

• Guards — Fn(&C, &Event, &Value) -> Result<bool>: the context, the event and the guard’s static params. Composite guards (and, or, not, stateIn) are evaluated by the engine.
• Actions — Fn(&mut ActionScope<C>) -> Result<()>. ActionScope exposes context (&mut C), event, params, and the effect helpers raise(event) and emit(value).

Built-in actions

assign, raise, sendTo, sendParent, forwardTo, escalate, log, cancel, stopChild, spawnChild, emit and choose are built in. A JSON assign operates on the dynamic context; anything that must compute values from the event is a named action writing scope.context. The callback-style built-ins enqueueActions and pure are not supported: move them into named logic.

Failure is explicit

A guard that returns Err, or a missing implementation, is an error, not a silent false. A name the chart uses but the registry lacks is reported by start() as ImplementationMissing before any event runs. An action failure follows actionErrorPolicy (see policies).