mlua-flow-ir (workspace)

flow.ir IR + interpreter substrate for the mlua ecosystem. 7 Node kinds + 20 Expr ops, no I/O, no concurrency, no agent dispatch — pure substrate.

This workspace publishes two crates:

Crate	Role
flow-ir-core	Pure Rust schema + sync eval + Dispatcher trait (no mlua, no async)
mlua-flow-ir	Async runtime (AsyncDispatcher / eval_async, including Fanout join-mode support) + mlua module() binding. Re-exports flow-ir-core.

Host-side concerns (Spawner / Worker / Loop / AuthzPolicy / cp_state persist) live in the upstream mlua-swarm-engine crate. This workspace is intentionally substrate-only.

Design

• 7 Node kinds — Step { ref, in, out }, Seq { children }, Branch { cond, then, else }, Fanout { items, bind, body, join, out }, Loop { counter, cond, body, max }, Try { body, catch, err_at }, Assign { at, value }
• 20 Expr ops — read/literal (Path, Lit), comparison (Eq, Ne, Lt, Lte, Gt, Gte), boolean (Not, And, Or), existence (Exists), arithmetic (Add, Sub, Mul, Div, Mod), aggregate (Len, In), and the CallExtern hatch
• Discriminated — #[serde(tag = "kind")] / #[serde(tag = "op")] + deny_unknown_fields
• Dispatcher = callback — host provides concrete implementations (process spawn, mlua callback, MCP call, direct LLM, etc.)

Quick start

use mlua_flow_ir::{eval, Dispatcher, EvalError, Node};
use serde_json::{json, Value};

let node: Node = serde_json::from_value(json!({
    "kind": "step",
    "ref": "uppercase",
    "in": { "op": "path", "at": "$.input" },
    "out": { "op": "path", "at": "$.output" },
})).unwrap();

struct FixtureDispatcher;
impl Dispatcher for FixtureDispatcher {
    fn dispatch(&self, _ref: &str, input: Value) -> Result<Value, EvalError> {
        if let Value::String(s) = input {
            Ok(Value::String(s.to_uppercase()))
        } else {
            Ok(input)
        }
    }
}

let result = eval(&node, json!({ "input": "hello" }), &FixtureDispatcher).unwrap();
assert_eq!(result, json!({ "input": "hello", "output": "HELLO" }));

Roadmap

• v0.0.1–0.0.3 — pre-split prototype (single crate)
• v0.0.4 — workspace split: flow-ir-core (Pure Rust) + mlua-flow-ir (async + mlua)
• v0.1.x (current) — Expr::CallExtern hatch + Externs DI registry, Expr::Mod, canonical wire-format alignment (gte/lte, args/arg), Node::Loop / Node::Try / Node::Assign, RFC 9535-style bracket path notation. See CHANGELOG.md for the full per-release list.
• Future — JSON / YAML loader split into mlua-flow-json / mlua-flow-yaml sibling crates; engine integration via mlua-swarm-engine (Spawner / Worker / Loop / AuthzPolicy)

Publish order

flow-ir-core first, then mlua-flow-ir (depends on flow-ir-core via path+version).

License

MIT OR Apache-2.0