#!/usr/bin/ruby
def wtf()
  x = 1
  def inc_x()
    x += 1
    x
  end
  inc_x()
  x
end
puts "Hello world: " + wtf().to_s
# Result is:
#./stupid.rb:5:in `inc_x': undefined method `+' for nil:NilClass (NoMethodError)
#        from ./stupid.rb:8:in `wtf'
#        from ./stupid.rb:11:in `<main>'