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Typed System One layer for Rust (Choice/Score/Noul).
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S1
A Rust derive layer for typed System One decisions: enums and structs become Choice, Score, and Noul questions with compile-time-checked, confidence-gated answers, plus a scriptable fake client for network-free tests.
- Stars
- 1
- Language
- Rust
- License
- MIT
- Reading time
- 3 min
- Published by
- Community
- Author
- AbdelStark
- Last verified
- Sep 2026
About this project
Typed System One decisions for Rust. Turn enums and structs into Choice, Score, and Noul questions. Get compile-time-checked, confidence-gated answers back. Add a Department::Legal variant and the match stops compiling until you handle it. A complete, network-free version of this snippet lives in examples/triage.rs and runs against s1-test::FakeClient. The typed layer is this git workspace (s1, s1-derive, s1-test). HTTP transport is the published typesafe-rs crate. From a checkout of this repo:
Quoted from the project's README. Read the full README.
Highlights
- Derive macros turn enums into Choice and Score questions and structs into typed question sets; adding a variant breaks the match until handled.
- Policy maps confidence onto Verdict::Act, Review, or Escalate, with per-variant thresholds and a NoulPolicy for yes/no questions.
- HTTP is not in this crate: enable backend-typesafe-rs to use the published typesafe-rs client, or use s1-test::FakeClient.
- MSRV is 1.85 (edition 2024), and every crate in the workspace has #![forbid(unsafe_code)].
- The triage and moderation examples run entirely through FakeClient: no network call and no API key.
Quickstart
rust
#[derive(Choice)]
#[s1(instructions = "Which team should handle this ticket?")]
enum Department {
#[s1("Payment, invoice, refund, or subscription issues")]
Billing,
#[s1("Bugs, errors, or integration problems")]
Technical,
}Watch out
Dual-licensed under Apache-2.0 or MIT. The typed layer is a git workspace rather than a published crate, HTTP lives in the separate typesafe-rs crate, and live use needs TYPESAFE_API_KEY.
Questions about this entry
Short answers drawn from the linked project or page.
Yes, and that is the catch. The typed layer is a git workspace, not a published crate, so s1 and s1-derive come from a git URL. Only the HTTP transport is published, as the separate typesafe-rs crate, and it only implements the backend trait behind the backend-typesafe-rs feature.
Yes. s1-test provides a scriptable FakeClient, and both the triage and moderation examples run entirely through it with no key and no network. Handlers match on the question-key set from the derived questions() call and go through QuestionSet::decode and S1::ask rather than a hand-rolled decoder.
You get a typed error rather than a surprise: an unrecognised Choice label decodes as DecodeError::UnknownLabel, out-of-range scores and noul values as DecodeError::OutOfRange, and a missing answer as DecodeError::MissingAnswer. Add an enum variant and your existing match stops compiling until you handle it.
Yes. Policy enforces act greater than or equal to review and every threshold inside 0 to 1. The infallible constructors panic on violation, while try_act, try_review, and try_for_variant return a PolicyError instead. A Policy maps one scalar, the API confidence by default, onto Verdict::Act, Verdict::Review, or Verdict::Escalate.
Derive Choice on a fieldless enum with 2 to 255 variants, Score on a fieldless enum where declaration order is the level index, and Questions on a named struct of those plus a bool annotated with #[s1(noul = "...")]. Each Choice and Score variant needs a description unless you set allow_empty_descriptions.
Enable the backend-typesafe-rs feature so typesafe-rs 0.1 implements DecisionBackend, then build a client with Client::from_env(). It reads TYPESAFE_API_KEY as required plus optional TYPESAFE_BASE_URL and TYPESAFE_DEFAULT_MODEL; retries, timeouts, and identification headers live in typesafe-rs, not this crate.
Noul uses its own NoulPolicy::new with four thresholds, for example 0.9, 0.15, 0.35, 0.65, mapping the probability onto Act(true), Act(false), Review, or Escalate. A Score answer offers nearest() for the closest level and expected() for the probability-weighted index.
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