def short_out(io,level)
      io.write("[")
      @children.each_with_index do |child , i|
        child.out(io , level + 1 )
        io.write ", " unless (i+1) == @children.length
      end
      io.write("]")
    end
def short_out(io,level)
      io.write("[")
      @children.each_with_index do |child , i|
        child.out(io , level + 1 )
        io.write ", " unless (i+1) == @children.length
      end
      io.write("]")
    end
This defines the short output which is basically what you would write in ruby
 ie [ value1 , value2 , ...]
 The short is used for 7 or less SimpleNodes