hello_world.rb

require 'lily/adapter/rack'
require 'lily/application/routed_application'

handler = RoutedApplication.new(:routes => [[:GET, '/', 'Hello world']])
run Lily::Adapter::Rack::Handler.new(:handler => handler)
# Or closer to PHP version: Lily::Adapter::Rack.new(:runner => method(:run)).run(:handler => handler)

hello_world_alt.rb

require 'lily/adapter/rack'
require 'lily/application/routed_application'

handler = RoutedApplication.new(:routes => [[:GET, '/', 'Hello world']])
run Lily::Adapter::Rack::Handler.new(:handler => handler)

lily.rb

require 'lily/adapter/rack'
require 'lily/util/response'

class Application
  include Lily::Util::Response

  def call(request)
    ok("Hello World")
  end
end

run Lily::Adapter::Rack::Handler.new(:handler => Application.new)
# Or closer to PHP version: Lily::Adapter::Rack.new(:runner => method(:run)).run(:handler => Application.new)