require 'tk'

root = TkRoot.new { title "Hello, World!" }
TkLabel.new(root) do
   text 'Hello, World!'
   pack { padx 15 ; pady 15; side 'left' }
end
Tk.mainloop

NoMethodError: undefined method `include?' for nil:NilClass
---< backtrace of Ruby side >-----
/home/mateusz/.gem/ruby/1.9.1/gems/arcadia-1.1.0/ext/ae-editor/ae-editor.rb:4411:in `on_before_run_cmd'
/home/mateusz/.gem/ruby/1.9.1/gems/arcadia-1.1.0/lib/a-commons.rb:788:in `block in _process_fase'
/home/mateusz/.gem/ruby/1.9.1/gems/arcadia-1.1.0/lib/a-commons.rb:786:in `each'
/home/mateusz/.gem/ruby/1.9.1/gems/arcadia-1.1.0/lib/a-commons.rb:786:in `_process_fase'
/home/mateusz/.gem/ruby/1.9.1/gems/arcadia-1.1.0/lib/a-commons.rb:701:in `block in process_event'
/home/mateusz/.gem/ruby/1.9.1/gems/arcadia-1.1.0/lib/a-commons.rb:699:in `each'
/home/mateusz/.gem/ruby/1.9.1/gems/arcadia-1.1.0/lib/a-commons.rb:699:in `process_event'
/home/mateusz/.gem/ruby/1.9.1/gems/arcadia-1.1.0/lib/a-core.rb:1490:in `block in initialize'
/usr/lib/ruby/1.9.1/tk.rb:1451:in `call'
/usr/lib/ruby/1.9.1/tk.rb:1451:in `eval_cmd'
/usr/lib/ruby/1.9.1/tk.rb:1451:in `cb_eval'
/usr/lib/ruby/1.9.1/tk.rb:1398:in `call'
/usr/lib/ruby/1.9.1/tk.rb:1594:in `block in callback'
/usr/lib/ruby/1.9.1/tk.rb:1593:in `catch'
/usr/lib/ruby/1.9.1/tk.rb:1593:in `callback'
/usr/lib/ruby/1.9.1/tk.rb:1300:in `mainloop'
/usr/lib/ruby/1.9.1/tk.rb:1300:in `block in <module:TkCore>'
---< backtrace of Tk side >-------
    invoked from within
"rb_out c00395"
    invoked from within
".w00000.topf.tb0.w00266 invoke "
    invoked from within
".w00000.topf.tb0.w00266 instate !disabled { .w00000.topf.tb0.w00266 invoke } "
    invoked from within
".w00000.topf.tb0.w00266 instate pressed { .w00000.topf.tb0.w00266 state !pressed; .w00000.topf.tb0.w00266 instate !disabled { .w00000.topf.tb0.w00266 ..."
    (command bound to event)