From: Chad Perrin <perrin@...>
Date: 2006-08-02T05:58:15+09:00
Subject: Re: I thought this was the one that worked?

On Wed, Aug 02, 2006 at 05:41:46AM +0900, ara.t.howard@noaa.gov wrote:
> On Wed, 2 Aug 2006, Chad Perrin wrote:
> 
> >>that's an absurd thing to say don't you think?  it's not bad or good - it
> >>is what it is.  it is in fact a very pure closure which perfectly captures
> >>the state in which it was defined in.  note that i said it captures the
> >>'state' and not the 'state of the state' - in otherwords it has a pointer
> >>to the state and not a copy of the state.  that way it even has access to
> >>newly added information as my example shows.  this is amazingly powerful
> >>even if it doesn't fit your idea of what a closure may or may not be.
> >
> >No, I don't think it's "an absurd thing to say" -- it just doesn't have 
> >much
> >depth.  The depth is this:
> >
> >If it doesn't provide what OOPish programmers would call "protection", it's
> >not a closure.  How can it be a closure if it's not closed?
> 
> because 'enclose' does not imply 'closed forever':

We're discussing "closures", not "enclosures".
> 
>   en·close   Audio pronunciation of "enclose" ( P )  Pronunciation Key  
>   (n-klz) also in·close (n-)
>   tr.v. en·closed, en·clos·ing, en·clos·es
> 
>      1. To surround on all sides; close in.
> 
>      2. To fence in so as to prevent common use: enclosed the pasture.
> 
>      3. To contain, especially so as to envelop or shelter: “Every one of
>      those darkly clustered houses encloses its own secret” (Charles 
>      Dickens).
> 
>      4. To insert into the same envelope or package: enclose a check with 
>      the
>      order.

Two definitions of "closure" from the American Heritage Dictionary of
the English Language:

  A bringing to an end; a conclusion: finally brought the project to
  closure.

  The property of being mathematically closed.

In fact, the term "closure" in computer science is derived from the
mathematical definition of "closure", as in "a closed system".  A
closure in computer science is code and data that constitute a closed
system.  As David has suggested (without specifically and explicitly
saying it outright in such terms), the data in question might consist of
a sort of "potential data" such that a closure's referent closed scope
needn't necessarily actually contain anything, so long as the scope
itself is theoretically present and accounted for.

> 
> i think the critical thing you are muddying the waters with is the fact that
> no definition of enclosure implies and sort of static or frozen jail like
> container.  consider the phrase

If anything, it's you who's introducing pollutants to the otherwise
clearer (if not actually clear) subject by confusing "enclosure" with
"closure".

-- 
CCD CopyWrite Chad Perrin [ http://ccd.apotheon.org ]
"There comes a time in the history of any project when it becomes necessary
to shoot the engineers and begin production." - MacUser, November 1990