From: Robert Klemme <shortcutter@...>
Date: 2010-12-27T20:39:46+09:00
Subject: Re: converting traversal fn into Enumeration

On Sun, Dec 26, 2010 at 8:42 AM, Fearless Fool <r@alum.mit.edu> wrote:
> I've not quite wrapped my head around Enumerations, but I suspect I'm
> just being dense.  Assume the following small code fragment:
> -----
> TNode = Struct.new(:left, :right, :value)
> class TNode
>
>  def traverse(&block)
>    left.traverse(&block) if left
>    right.traverse(&block) if right
>    yield(self)
>  end

Is this really the order that you want?  Typically the current node is
visited between left and right to get an in order tree traversal:

 def traverse(&block)
   left.traverse(&block) if left
   yield(self)
   right.traverse(&block) if right
 end

If you need the result visiting the current node you can store it in a
variable and return it at the end.

Since you yield node instances themselves in #traverse it seems more
natural to implement #each like this:

class TNode
  include Enumerable

  def each(&b)
    left.each(&b) if left
    yield value
    right.each(&b) if right
    self # according to convention of #each
  end
end

> ... but as I mentioned, I haven't figured out the right way to structure
> this.  Any hints?  Or is it not worth the effort?

See above.

Kind regards

robert

-- 
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