From: Chad Perrin <perrin@...>
Date: 2006-08-01T12:26:13+09:00
Subject: Re: I thought this was the one that worked?

On Tue, Aug 01, 2006 at 11:39:29AM +0900, Hal Fulton wrote:
> Chad Perrin wrote:
> >
> >Am I to assume that some_local_variable is going out of scope outside of
> >the lambda declaration at some point, to create that closure?
> >
> >
> >
> >>   All things that are called "blocks" in Ruby are closures.
> >>   Do you still have any questions on the matter?
> >
> >
> >Yes.  Are you just failing to explain how these things are closures, or
> >do you not know what a closure is?  You keep telling me blocks are
> >closures somehow, but you're not explaining how.  Saying it doesn't make
> >it so.  Please explain what I'm missing.
> >
> 
> I'm unfamiliar with your assertion that the context has to go
> out of scope before a closure exists.
> 
> Not trying to argue, just stating my perception.
> 
> Maybe you can point us to a formal definition somewhere.

How's this?:
  
  Closure
      A "closure" is an expression (typically a function) that can have
      free variables together with an environment that binds those
      variables (that "closes" the expression).

I found it on this page:

  http://jibbering.com/faq/faq_notes/closures.html

I also found this:

  http://www.perl.com/pub/a/2002/05/29/closure.html


> 
> I would have said that a closure *will* retain its variables
> *if/when* they go out of scope.
> 
> Bad analogy: We might loosely define a car as "a machine that
> goes places," but it's still a car even when it sits still.

My understanding is that the vehicle is a car, and the use of it is a
drive (to the country, or whatever).  Similarly, a block of code that
can be passed around like a first-class member is a block, or lambda, or
whatever you want to call it today: if you pass it to a function as an
argument, it's a callback, and if you lexically close it, it's a
closure.


> 
> My impression is that you're applying the definition too
> rigidly.

I suppose that's possible, but I really don't think so.  Do you have a
formal definition of a closure that specifically contradicts my
understanding?

-- 
CCD CopyWrite Chad Perrin [ http://ccd.apotheon.org ]
"A script is what you give the actors.  A program
is what you give the audience." - Larry Wall