An example of 'slices' implementation in 37 lines of pure Sinatra.

sinatra_slices_example.rb

require 'sinatra/base'

module Sinatra

  module Slice
    def self.prefix_routes(middleware)
      prefix = prefix_from(middleware)
      middleware.instance_eval {
        @routes.each do |http_method, _|
          @routes[http_method].each_with_index do |route, index|
            original_route = route.shift.source[1..-1]
            @routes[http_method][index] = [
              Regexp.compile('^/' + prefix + (original_route == "/$" ? '$' : original_route))
            ] + route
          end
        end
      }
      middleware
    end

    private
    def self.prefix_from(klass)
      klass.name.gsub(/::/, '/').
        gsub(/([A-Z]+)([A-Z][a-z])/,'\1_\2').
        gsub(/([a-z\d])([A-Z])/,'\1_\2').
        tr("-", "_").
        downcase.split('_')[0..-2].join('\/')
    end
  end

  class Base
    class << self
      alias_method :original_use, :use
      def use(middleware, *args, &block)
        original_use(Slice.prefix_routes(middleware), *args, &block)
      end
    end
  end

end

class UserProfilesModule < Sinatra::Base

  # GET /user/profiles
  get '/' do
    'index action'
  end

  # GET /user/profiles/:id
  get '/:id' do
    'show action'
  end

  # GET /user/profiles/:id/edit
  get '/:id/edit' do
    'edit action'
  end

end

class TestApp < Sinatra::Base

  use UserProfilesModule

  # GET /
  get '/' do
    'Hello from index app'
  end
end