From: Christoph Schmitz <chs@...>
Date: 2002-12-29T20:56:58+09:00
Subject: yield and recursion

Hi all,

I was just trying to grasp the concept of iterators, and
the first thing I tried was an iterator for a binary tree.

What I came up with is something like

class Node
....
	def inorder
		@left.inorder unless @left.nil?
		yield @value
		@right.inorder unless @right.nil?
	end
end

@left, @right and @value being the obvious fields. This doesn't
work as intended, though. (LocalJumpError IIRC).

So I tried this:

class Node
....
	def inorder_block (block)
		@left.inorder_block (block) unless @left.nil?
		block.call(@value)
		@right.inorder_block (block) unless @right.nil?
	end

	def inorder_yield 
		inorder_block { |value| yield value }
	end
end

Now I can write

aNode.inorder_yield { |v| ... do something with v ... }

It looks to me that the second version is just an unrolled
way of writing the first one. Can anyone tell me what the difference
is?

Thanks in advance,
Christoph