statum

statum is about representational correctness when a value's phase should change what methods are legally available on that value. It helps make invalid, undesirable, or not-yet-validated states impossible to represent as ordinary values.

It applies the same idea as Option and Result: absence or failure becomes explicit in the type instead of staying implicit in the program.

This crate re-exports:

• attribute macros: #[state], #[machine], #[transition], #[validators]
• runtime types: statum::Error, statum::Result<T>
• advanced traits: StateMarker, UnitState, DataState, CanTransition*
• typed introspection and runtime-join surfaces: MachineIntrospection, MachineGraph, MachineTransitionRecorder, MachinePresentation
• projection helpers: statum::projection

Install

[dependencies]
statum = "0.8.10"

Statum targets stable Rust and currently supports Rust 1.93+.

Mental Model

• Use statum when pressing . before and after a phase change should show a meaningfully different method surface.
• Durable workflows and protocols are one strong fit. Staged validation, resolution, and build surfaces are another.
• #[state] defines the legal phases
• #[machine] defines the durable context
• #[transition] defines the legal edges
• #[validators] rebuilds typed machines from stored data

Minimal Example

use statum::{machine, state, transition};

#[state]
enum LightState {
    Off,
    On,
}

#[machine]
struct Light<LightState> {
    name: String,
}

#[transition]
impl Light<Off> {
    fn switch_on(self) -> Light<On> {
        self.transition()
    }
}

#[transition]
impl Light<On> {
    fn switch_off(self) -> Light<Off> {
        self.transition()
    }
}

# fn main() {}

Docs

• Machine introspection is useful when the machine definition should also drive CLI explainers, graph exports, generated docs, branch-strip views, or runtime replay/debug tooling. Statum exposes exact transition sites instead of a coarse machine-wide state list.
• API docs: https://docs.rs/statum
• Repository README: https://github.com/eboody/statum/blob/main/README.md
• Validators guide: https://github.com/eboody/statum/blob/main/docs/persistence-and-validators.md
• Examples crate: https://github.com/eboody/statum/tree/main/statum-examples
• Repository: https://github.com/eboody/statum