Visitor without relying on Rubinius::AST::Node#visit.

visitor.rb

class Visitor
  attr_reader :output

  def initialize
    @output = ""
  end

  def visit(node)
    send node.node_name, node
  end

  def array_literal(o)
    emit '['
    o.body.each_with_index do |n, idx|
      visit n
      emit ', ' unless o.body.length - 1 == idx
    end
    emit ']'
  end

  def fixnum_literal(o)
    emit "#{o.value}"
  end

  def local_variable_assignment(o)
    emit "var #{o.name} = "
    visit(o.value)
    emit ";"
  end

  def emit(str)
    @output << str
  end
end

ast = "a = [1,3]".to_ast
visitor = Visitor.new
visitor.visit ast
puts visitor.output