$ ruby treedumper.rb 
/usr/home/pope/.rvm/gems/ruby-1.8.7-p248/gems/antlr3-1.8.5/lib/antlr3/dot.rb:122:in `define_nodes': undefined method `node_number' for #<ANTLR3::DOT::TreeGenerator:0x2d1ab058> (NoMethodError)
        from /usr/home/pope/.rvm/gems/ruby-1.8.7-p248/gems/antlr3-1.8.5/lib/antlr3/dot.rb:110:in `to_dot'
        from /usr/home/pope/.rvm/gems/ruby-1.8.7-p248/gems/antlr3-1.8.5/lib/antlr3/dot.rb:93:in `generate'
        from treedumper.rb:9