rust-elm 0.3.0

Elm Architecture for Rust: composable reducers, pure effects, async runtime.
Documentation

rust-elm 0.3.0

Elm Architecture for Rust, evolving toward The Composable Architecture (UDF).

Install

[dependencies]
rust-elm = { path = "../rust-elm" }
rust-elm = "0.3.0"
rust-key-paths = "3.3.1"
key-paths-derive = "3.2.0"
tokio = { version = "1.38", features = ["rt-multi-thread", "macros"] }

Feature flags

Feature Default Purpose
runtime yes Tokio interpreter, Runtime, Store, subscriptions
websocket yes Real Sub::websocket via tokio-tungstenite (interval stub without it)
serde no FileStorage, replay snapshots

Build without Tokio (pure descriptions only):

cargo build -p rust-elm --no-default-features

Quick start

use rust_elm::{Cmd, Program, Runtime, RuntimeConfig, Sub, Environment};

#[derive(Default)]
struct State { count: i32 }

fn init() -> (State, Cmd<i32>) {
    (State::default(), Cmd::none())
}

fn update(state: &mut State, msg: i32) -> Cmd<i32> {
    state.count += msg;
    Cmd::none()
}

fn subscriptions(_: &State) -> Sub<i32> {
    Sub::none()
}

fn main() {
    let program = Program::new(init, update, subscriptions);
    let runtime = Runtime::from_program(program, Environment::new(), RuntimeConfig::new(64));
    let store = runtime.store();
    store.dispatch(1);
    runtime.shutdown();
}

Release notes

0.3.0

  • RuntimeConfig — bus_capacity, worker_threads, thread_name for Runtime::from_program.
  • RefKpTrait — scope/store/optics use core traits directly; StateLens / StateKeypath removed.
  • StoreTask::finish_with_timeout — configurable wait for store work.
  • pain example — ISO 20022-style validation with fail-fast Validator.

0.2.0

  • WebSocket subscriptions, runtime feature flags, ecommerce example.

Modules

Module Purpose
cmd Commands returned from update
effect Pure async effect descriptions (debounce, throttle, from_run, cancel)
sub Subscription descriptions (runtime-agnostic data)
reduce_panic catch_reduce_panic, catch_reduce, ReducePanic
runtime Bus-driven update loop + Tokio interpreter (runtime feature)
subscription Sub interpreter — tick/stream/websocket (runtime feature)
store Store, StoreTask, ScopedStore, state subscription (runtime feature)
test_store ExhaustiveTestStore for synchronous effect/action testing
test_runtime Sync testing without Tokio
shared Shared<T>, Storage, InMemoryStorage, FileStorage (serde)
dependencies Re-exports rust_dependencies
env Environment (live/test), FakeClock, MockHttp
optics State/action focusing via rust-key-paths
reducer Reducer trait, CombineReducers (up to 6 siblings), reducers!
scope ScopeReducer, IfLetReducer, ForEachReducer, lift_cmd
identified Re-exports rust_identified_vec
replay Action log + replay harness

Examples (one per feature area)

Example Command Shows
catch_reduce cargo run -p rust-elm --example catch_reduce Panic: default vs rollback
subscriptions cargo run -p rust-elm --example subscriptions Tick + map_msg subs
scope_for_each cargo run -p rust-elm --example scope_for_each Scope + ForEach without Runtime
dependencies cargo run -p rust-elm --example dependencies Environment live vs test
shared_state cargo run -p rust-elm --example shared_state Shared<T> observers
ecommerce cargo run -p rust-elm --example ecommerce Full shop (all features)

Quality tooling

# Clippy (crate only)
cargo clippy -p rust-elm --all-targets --no-deps -- -D warnings

# Miri (identified, shared, scope — no runtime)
./scripts/miri-rust-elm.sh

# Scope / ForEach benchmarks
cargo bench -p rust-elm --bench scope_dispatch

Key paths prelude

use rust_elm::keypath::{Kp, KpTrait, RefKpTrait, Readable, Writable};
use key_paths_derive::Kp;

See ROADMAP.md, book/architecture.md, book/ecommerce.md.