From: "maillist@..." <maillist@...>
Date: 2003-07-17T10:59:31+09:00
Subject: Re: callbacks in ruby and using yield in resursion

It works! Thanks very much. One thing I don't get...  what exactly is
the &block, is it a reserved work, a predefined variable or what???

On Thu, 2003-07-17 at 13:08, Joel VanderWerf wrote:
> Paul wrote:
> > Hi,
> > 
> > How do I pass a ruby function as an argument to another ruby function so
> > that it can be used as a callback?
> > 
> > Also, I have a recursive tree traversing function that I would like to
> > use yield with. For example:
> > 
> > def run(parent,level)
>    def run(parent, level, &block)
> > 	....
> > 	yield parent
>          block.call(parent)
> > 	....
> > 	run(child,level+1)#yield????????
>          run(child,level+1, &block)
> > 	....
> > end
> > 
> > run(root,0){|node|
> > 	puts node.get_name
> > }
> > 
> > It will not work because i cant use the yield in the recursive call to
> > run.
> 
> The first use of the "&block" notation converts the caller-supplied 
> block to an instance of Proc and stores it in "block".
> 
> The second use of "&block" passes the proc object as the caller-supplied 
> block of the recursive call to #run.
>