Lemon — reactive native desktop UI in Rust.

Getting started

Most apps only need [run], [WindowConfig], [Cx], and the layout widgets ([Column], [Row], [Text], [Button], …) re-exported below.

use lemon::{run, Cx, WindowConfig};
use lemon::{Button, Column, Text};

fn app(cx: &Cx) -> lemon::element::Element {
    let count = cx.use_signal(0i32);
    let label = count.clone();
    let inc = count.clone();
    Column::new()
        .child(Text::new(move || label.get().to_string()))
        .child(Button::new("+").on_click(move || inc.update(|n| *n += 1)))
        .into_element()
}

fn main() {
    run(WindowConfig::default().title("Counter"), app);
}

How an update flows

1. Your root function (app) returns an [element::Element] tree built with builders.
2. [Cx::use_signal] and dynamic [Text::new] closures subscribe to reactive state.
3. When state changes, the runtime diffs the previous tree against the new one and emits patches.
4. The platform layer applies patches to a retained tree, runs layout (Taffy), then paints (Vello).

Keys and lists

Give stable .key(id) values to siblings that are inserted, removed, or reordered (see the list_keyed example). Without keys, children are reconciled by index only.

Components

[Component::new] wraps a sub-view with its own [Cx] hooks. It currently takes a function pointer (fn(&Cx) -> Element), not a capturing closure. For list rows with per-item state, prefer keyed [Row] / [Column] children instead of capturing [Component]s.

Migrating from Box_

The generic flex container builder was renamed to [View] (and [Element::View]) because Box clashes with [std::boxed::Box] in Rust. Update imports and matches:

[Box_] remains available as a deprecated type alias for one release cycle. Roadmap issues and older examples may still mention Box_; treat that name as [View].

Lower-level API

[Runtime], [RetainedTree], [layout_pass], and [paint_pass] are public for tests and custom hosts; normal apps should use [run] and never touch those directly.