NimUI

SwiftUI-style declarative UI DSL for Nim — targets HTML/CSS via the Nim JS backend.

NimUI lets you build web frontends entirely in Nim. Describe your UI with a declarative DSL inspired by SwiftUI, compile it to JavaScript with nim js, and render it in the browser.

Features

• Declarative DSL — Text, VStack, HStack, Button with a SwiftUI-like syntax
• Modifier chains — .padding(), .foregroundColor(), .font() and more
• HTML/CSS output — renders to semantic HTML with inline styles and hashed CSS classes
• XSS-safe — user text is HTML-escaped by default
• Event handlers — Button actions compile to JavaScript <script> blocks
• Zero runtime dependencies — ships a single JS file

Requirements

• Nim >= 1.6.0

Quick Start

Install

nimble install nimui

Write a UI

import nimui
import nimui/modifiers

let doc = App:
  VStack:
    Text("Hello, World!")
      .padding(16)
      .foregroundColor("#333")
      .font(24)
    HStack:
      Text("Welcome to ")
        .foregroundColor("#666")
      Text("NimUI")
        .foregroundColor("#007acc")
        .font(20)
    Button(text = "Click me"):
      echo "Button clicked!"

document.body.innerHTML = doc.render().cstring

Build

nim js -o:build/app.js src/main.nim

Then include the output JS in an HTML page.

Build Tasks

Command	Description
nimble build	Build the NimUI library (JS backend)
nimble buildExample	Build the hello-world example
nimble test	Run unit tests (C backend)
nimble testJs	Smoke test — compile to JS
nimble clean	Remove build artifacts

Architecture

nimui.nim          — Public API entry point; re-exports macros and runtime types
nimui/
  core.nim         — Domain entities (RootView, Modifier, Handler)
  render.nim       — HTML rendering (string concatenation, HTML escaping)
  modifiers.nim    — UFCS modifier procs (.padding, .foregroundColor, .font)
nimui.js           — JavaScript runtime support

The ui macro collects view declarations at compile time into a UiBuilder. At runtime, render() walks the view tree and produces an HTML fragment.

Project Status

v0.1.0 — MVP. Core components (Text, VStack, HStack, Button) and basic modifiers are implemented. See aidlc-docs/ for design documentation.

Disclaimer

⚠️ Experimental — Under Active Development

NimUI is an experimental project (v0.1.0) and is still under active development. Not all features are stable, and the API may change without notice.

Relation to SwiftUI

NimUI is inspired by SwiftUI's declarative syntax but is not a full reimplementation of SwiftUI. The following major SwiftUI features are not yet supported:

Category	SwiftUI Feature	Status
Layout	List, Form, ScrollView	❌ Not implemented
	LazyVStack, LazyHStack, Grid	❌ Not implemented
	Spacer, Divider	❌ Not implemented
Navigation	NavigationView, NavigationLink	❌ Not implemented
	TabView, Sheet, FullScreenCover	❌ Not implemented
State Management	@State, @Binding	❌ Not implemented
	@ObservedObject, @EnvironmentObject	❌ Not implemented
	@Environment	❌ Not implemented
Controls	Toggle, Slider, Stepper	❌ Not implemented
	Picker, TextField, SecureField	❌ Not implemented
	TextEditor, DatePicker, ColorPicker	❌ Not implemented
Modifiers	.frame(), .background(), .overlay()	❌ Not implemented
	.border(), .shadow(), .clipShape()	❌ Not implemented
	.rotation(), .scale(), .animation()	❌ Not implemented
	.transition(), .gesture()	❌ Not implemented
	.onAppear(), .onDisappear()	❌ Not implemented
Styling	Color, Font, Image	❌ Not implemented
	Shape (Circle, Rectangle, etc.)	❌ Not implemented
Accessibility	.accessibilityLabel(), .accessibilityHint()	❌ Not implemented
Advanced	ForEach, conditional ViewBuilder	❌ Not implemented
	matchedGeometryEffect, preference	❌ Not implemented
	onChange	❌ Not implemented

This list is not exhaustive. Contributions are welcome!

License

BSD 3-Clause. See LICENSE for details.