[ruby-talk:6513] Question about the behavior of write attributes in blocks

Hi,

I am trying to understand iterators and blocks in Ruby.  Could someone
explain to me the logic behind the output

>try fail fail
>succ succ succ

of the following program? How can I fix my tree class to get the ``right''
behavior?

***********************
# A binary tree class
class Bt
        def  initialize( cont, l = nil, r = nil )
                @data=cont
                @left=l
                @right=r
        end
        def each
              yield data
              left.each   { |l| yield l }
              right.each { |r| yield r }
        end
        attr_accessor( :left,  :right, :data)
end

module Each
        def each
        end
end

nil.extend(Each)

root = Bt.new ( "fail ", Bt.new "fail ", Bt.new "fail ")
root.data="try "                            # ``data'' is changed
root.each { |a|  a = "try " }            #  ``data''  is not changed
root.each { |a|  print a  }
puts
root.each { |a|  a.replace "succ " } # ``data'' is changed
root.each { |a|  print a  }
*****************************************
Thanks,
        Christoph