Crate lemon 

Lemon — reactive native desktop UI in Rust.

Getting started

Most apps only need run, WindowConfig, Cx, and the layout widgets (Column, Row, Text, Button, …). Import them via prelude:

use lemon::prelude::*;

fn app(cx: &Cx) -> Element {
    let count = cx.use_signal(0i32);
    let label = count.clone();
    let inc = count.clone();
    Column::new()
        .children(children![
            Text::new(move || label.get().to_string()),
            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 keys 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 Components.

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:

Before	After
Box_::new()	View::new()
Element::Box_(…)	Element::View(…)
use …::{Box_, …}	use …::{View, …}

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.

Re-exports

pub use asset::ImageHandle;

pub use element::builders::Button;

pub use element::builders::Column;

pub use element::builders::Component;

pub use element::builders::Row;

pub use element::builders::Text;

pub use element::builders::View;

pub use element::builders::View as Box_;

pub use element::events::Cursor;

pub use element::events::KeyEvent;

pub use element::events::KeyState;

pub use element::events::LemonKey;

pub use element::events::Modifiers;

pub use element::events::NamedKey;

pub use element::style::Color;

pub use element::style::Overflow;

pub use element::style::StyleProps;

pub use layout::layout_pass;

pub use layout::layout_pass_if_dirty;

pub use layout::LayoutMap;

pub use layout::LayoutRect;

pub use layout::Viewport;

pub use paint::paint_pass;

pub use paint::PaintStats;

pub use platform::run;

pub use platform::AppState;

pub use platform::WindowConfig;

pub use retained::RetainedTree;

pub use runtime::cx::Cx;

pub use runtime::signal::Signal;

pub use runtime::Runtime;

pub use debug::Category as DebugCategory;

Modules

asset

debug

Opt-in verbose tracing for debugging Lemon’s reactive pipeline.

diff

element

layout

paint

platform

Platform layer: winit window, wgpu surface, Vello renderer, and frame loop.

prelude

Commonly used types for Lemon applications.

retained

runtime

Macros

children

Builds a Vec<Element> from heterogeneous widget builders.

lemon_trace

Log with format! args when cat is enabled.