rooibos 0.6.0

Confidently Build Terminal Apps

Rooibos helps you build interactive terminal applications. Keep your code understandable and testable as it scales. Rooibos handles keyboard, mouse, and async work so you can focus on behavior and user experience.

gem install rooibos

Currently in beta. APIs may change before 1.0.

Get Started in Seconds

rooibos new my_app
cd my_app
rooibos run

That’s it. You have a working app with keyboard navigation, mouse support, and clickable buttons. Open lib/my_app.rb to make it your own.

---

The Pattern

Rooibos uses Model-View-Update, the architecture behind Elm, Redux, and Bubble Tea. State lives in one place. Updates flow in one direction. The runtime handles rendering and runs background work for you.

---

Hello, MVU

The simplest Rooibos app. Press any key to increment the counter. Press Ctrl+C to quit.

require "rooibos"

module Counter
  # Init: How do you create the initial model?
  Init = -> { 0 }

  # View: What does the user see?
  View = -> (model, tui) { tui.paragraph(text: <<~END) }
    Current count: #{model}.
    Press any key to increment.
    Press Ctrl+C to quit.
  END

  # Update: What happens when things change?
  Update = -> (message, model) {
    if message.ctrl_c?
      Rooibos::Command.exit
    elsif message.key?
      model + 1
    end
  }
end

Rooibos.run(Counter)

That’s the whole pattern: Model holds state, Init creates it, View renders it, and Update changes it. The runtime handles everything else.

---

Your First Real Application

A file browser in sixty lines. It opens files, navigates directories, handles errors, styles directories and hidden files differently, and supports vim-style keyboard shortcuts. If you can do this much with this little code, imagine how easy your app will be to build.

require "rooibos"

module FileBrowser
  # Model: What state does your app need?
  Model = Data.define(:path, :entries, :selected, :error)

  Init = -> {
    path    = Dir.pwd
    entries = Entries[path]
    Ractor.make_shareable( # Ensures thread safety
      Model.new(path:, entries:, selected: entries.first, error: nil))
  }

  View = -> (model, tui) {
    tui.block(
      titles: [model.error || model.path,
               { content: KEYS, position: :bottom, alignment: :right}],
      borders: [:all],
      border_style: if model.error then tui.style(fg: :red) else nil end,
      children: [tui.list(items: model.entries.map(&ListItem[model, tui]),
                          selected_index: model.entries.index(model.selected),
                          highlight_symbol: "",
                          highlight_style: tui.style(modifiers: [:reversed]))]
    )
  }

  Update = -> (message, model) {
    return model.with(error: ERROR) if message.error?
    model = model.with(error: nil) if model.error && message.key?

    if message.ctrl_c? || message.q? then Rooibos::Command.exit
    elsif message.home? || message.g? then model.with(selected: model.entries.first)
    elsif message.end? || message.G? then model.with(selected: model.entries.last)
    elsif message.up_arrow? || message.k? then Select[:-, model]
    elsif message.down_arrow? || message.j? then Select[:+, model]
    elsif message.enter? then Open[model]
    elsif message.escape? then Navigate[File.dirname(model.path), model]
    end
  }

  private # Lines below this are implementation details

  KEYS  = "↑/↓/Home/End: Select | Enter: Open | Esc: Navigate Up | q: Quit"
  ERROR = "Sorry, opening the selected file failed."

  ListItem = -> (model, tui) { -> (name) {
    modifiers = name.start_with?(".") ? [:dim] : []
    fg        = :blue if name.end_with?("/")
    tui.list_item(content: name, style: tui.style(fg:, modifiers:))
  } }

  Select = -> (operator, model) {
    new_index = model.entries.index(model.selected).public_send(operator, 1)
    model.with(selected: model.entries[new_index.clamp(0, model.entries.length - 1)])
  }

  Open = -> (model) {
    full = File.join(model.path, model.selected.delete_suffix("/"))
    model.selected.end_with?("/") ? Navigate[full, model] : Rooibos::Command.open(full)
  }

  Navigate = -> (path, model) {
    entries = Entries[path]
    model.with(path:, entries:, selected: entries.first, error: nil)
  }

  Entries = -> (path) {
    Dir.children(path).map { |name|
      File.directory?(File.join(path, name)) ? "#{name}/" : name
    }.sort_by { |name| [name.end_with?("/") ? 0 : 1, name.downcase] }
  }
end

Rooibos.run(FileBrowser)

---

Batteries Included

Commands

Applications fetch data, run shell commands, and set timers. Rooibos Commands run off the main thread and send results back as messages.

HTTP requests:

Update = -> (message, model) {
  case message
  in :fetch_users
    [model.with(loading: true), Rooibos::Command.http(:get, "/api/users", :got_users)]
  in { type: :http, envelope: :got_users, status: 200, body: }
    model.with(loading: false, users: JSON.parse(body))
  in { type: :http, envelope: :got_users, status: }
    model.with(error: "HTTP #{status}")
  end
}

Shell commands:

Update = -> (message, model) {
  case message
  in :list_files
    Rooibos::Command.system("ls -la", :listed_files)
  in { type: :system, envelope: :listed_files, stdout:, status: 0 }
    model.with(files: stdout.lines.map(&:chomp))
  in { type: :system, envelope: :listed_files, stderr:, status: }
    model.with(error: stderr)
  end
}

Timers:

Update = -> (message, model) {
  case message
  in { type: :timer, envelope: :tick, elapsed: }
    [model.with(frame: model.frame + 1), Rooibos::Command.wait(1.0 / 24, :tick)]
  end
}

And more! Rooibos includes all, batch, cancel, custom, exit, http, map, open, system, tick, and wait commands. You can also define your own custom commands for complex orchestration.

Every command produces a message, and Update handles it the same way.

Testing

Rooibos makes TUIs so easy to test, you’ll save more time by writing tests than by not testing.

Unit test Update, View, and Init. No terminal needed. Test helpers included.

def test_moves_selection_down_with_j
  model = Ractor.make_shareable(FileBrowser::Model.new(
    path: "/", entries: %w[bin exe lib], selected: "bin", error: nil))
  message = RatatuiRuby::Event::Key.new(code: "j")

  result = FileBrowser::Update.call(message, model)

  assert_equal "exe", result.selected
end

Style assertions. Draw to a headless terminal, verify colors and modifiers.

def test_directories_are_blue
  with_test_terminal(60, 10) do
    model = Ractor.make_shareable(FileBrowser::Model.new(
      path: "/", entries: %w[file.txt subdir/], selected: "file.txt", error: nil))
    widget = FileBrowser::View.call(model, RatatuiRuby::TUI.new)

    RatatuiRuby.draw { |frame| frame.render_widget(widget, frame.area) }

    assert_blue(1, 2) # "subdir/" at column 1, row 2
  end
end

System tests. Inject events, run the full app, snapshot the result.

def test_selection_moves_down
  with_test_terminal(120, 30) do
    Dir.mktmpdir do |dir|
      FileUtils.touch(File.join(dir, "a"))
      FileUtils.touch(File.join(dir, "b"))
      FileUtils.touch(File.join(dir, "c"))

      inject_key(:down)
      inject_key(:ctrl_c)

      # Tests use explicit params to inject deterministic initial state.
      Rooibos.run(
        model: Ractor.make_shareable(FileBrowser::Model.new(
          path: dir, entries: %w[a b c], selected: "a", error: nil)),
        view: FileBrowser::View,
        update: FileBrowser::Update
      )

      assert_snapshots("selection_moved_down") do |lines|
        title = "┌/tmp/test#{'─' * 107}┐"
        lines.map do |l|
          l.gsub(/┌#{Regexp.escape(dir)}[^┐]*┐/, title)
        end
      end
    end
  end
end

Snapshots record both plain text and ANSI colors. Normalization blocks mask dynamic content (timestamps, temp paths) for cross-platform reproducibility. Run UPDATE_SNAPSHOTS=1 rake test to regenerate baselines.

Scale Up

Large applications decompose into fragments. Each fragment has its own Model, View, Update, and Init. Parents compose children. The pattern scales.

The Router DSL eliminates boilerplate:

module Dashboard
  include Rooibos::Router

  route :stats, to: StatsPanel
  route :network, to: NetworkPanel

  keymap do
    key :ctrl_c, -> { Rooibos::Command.exit }
    only when: -> (model) { !model.modal_open } do
      key :q, -> { Rooibos::Command.exit }
      key :s, -> { StatsPanel.fetch_command }
      key :p, -> { NetworkPanel.ping_command }
    end
  end

  Update = from_router

  # ... Model, Init, View below
end

Declare routes and keymaps. The router generates Update for you. Use guards to ignore keys when needed.

CLI

The rooibos command scaffolds projects and runs applications.

rooibos new my_app    # Generate project structure
rooibos run           # Run the app in current directory

Generated apps include tests, type signatures, and a working welcome screen with keyboard and mouse support.

---

The Ecosystem

Rooibos builds on RatatuiRuby, a Rubygem built on Ratatui. You get native performance with the joy of Ruby. Rooibos is one way to manage state and composition. Kit is another.

Rooibos

Model-View-Update architecture. Inspired by Elm, Bubble Tea, and React + Redux. Your UI is a pure function of state.

• Functional programming with MVU

• Commands work off the main thread

• Messages, not callbacks, drive updates

Kit (Coming Soon)

Component-based architecture. Encapsulate state, input handling, and rendering in reusable pieces.

• OOP with stateful components

• Separate UI state from domain logic

• Built-in focus management & click handling

Both use the same widget library and rendering engine. Pick the paradigm that fits your brain.

---

Links

Get Started

Getting Started, Tutorial, Examples

Coming From…

React/Redux, BubbleTea, Textual

Learn More

Essentials, Scaling Up, Best Practices, Troubleshooting

Community

Discuss, Announcements, Bug Tracker, Contribution Guide, Code of Conduct

---

Website

rooibos.run

Source

git.sr.ht/~kerrick/rooibos

RubyGems

rubygems.org/gems/rooibos

© 2026 Kerrick Long · Library: LGPL-3.0-or-later · Website: CC-BY-NC-ND-4.0 · Snippets: MIT-0