AJAXy Sieve of Eratosthenes with Sinatra

config.ru

require 'index'

run Sinatra::Application

index.haml

!!!
%html{:xmlns => "http://www.w3.org/1999/xhtml"}
  %head
    %script{:type => "text/javascript", :src => "js/prototype.js"}
  %body
    %h1 Wieviele Primzahlen gibt es zwischen 0 und der Eingabe?
    %input{:type => 'text', :id => 'myval', :size => '10'}
    %input{:type => 'button', :value => 'Prime it!', :onClick => "ajaxRequest('/ajax', 'val='+$F('myval')); $('result').innerHTML = 'loading'"}
    #result

index.rb

require 'rubygems'
require 'sinatra'
require 'haml'
require 'timeout'

@@liste = {}

get '/' do
  haml :index
end

get '/ajax' do
  if request.xhr?
    n = params[:val].to_i
    if @@liste.has_key?(n)
      return @@liste[n]
     else
       begin
         Timeout.timeout 15 do
           neu = sieb(n)
           @@liste[n] = neu
           @output = neu.to_s
         end
       rescue Timeout::Error
         @output = "Timeout"
       end
       return @output
    end
  end
end

helpers do  
  def sieb(x)
    liste = []
    prim = []

    for i in (2..x) do
      liste << i
    end

    until liste.length == 0
      prim << liste[0]
      del = liste[0]
      
      for i in liste do
        if i % del == 0
          liste.delete(i)
        end
      end
    end
    return prim.length.to_s
  end  
end

prototype.js

Prototype in here