Yield and recursion

ruby-talk
1

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

2

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

Well, ruby don't propagate automatically the block.

The first time that you call #inorder the method has the block, but then
you call it without its block. This is why ruby give an error

Guy Decoux

3

class Node
def inorder(&block)
@left.inorder(block) unless @left.nil?
yield @value unless block.nil?
@right.inorder(block) unless @right.nil?
end
end

– Austin Ziegler, austin@halostatue.ca on 2002.12.29 at 13.08.00

···

On Sun, 29 Dec 2002 20:56:58 +0900, Christoph Schmitz wrote:

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

4

I also wrote a simple BinaryTree class to help me get started with Ruby.
You can find it at
http://people.cs.uct.ac.za/~flifson/things/Ruby/Misc/BinaryTree.rb and
maybe you can get some pointers/hints from it.

Farrel

···

–

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