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Modules vs name spaces (Was: Global namespace)

Erann Gat gat at jpl.nasa.gov
Thu Oct 30 17:25:15 EST 2003 
In article <pcoism6flxx.fsf at thoth.math.ntnu.no>, Harald Hanche-Olsen
<hanche at math.ntnu.no> wrote:

> | Modules work at compile time or run time depending on the module system.
> | 
> | Common Lisp has a package system but no module system (but it's possible
> | to add one -- see e.g. http://www.flownet.com/gat/locales.pdf).
> 
> Ah.  I had read that one before, but never realized that it describes
> a module system.  That gives me some idea what it's all about.
> Thanks.

I really should have called them modules, not locales.  (Maybe I'll change
the name in the next version.)  Locale nowadays has to do with
internationalization.  But I chose the name out of respect for the
original design in T.

> | Python has a module system that works at run-time, but no package system.
> | 
> | Does that help?
> 
> Now I am getting a bit confused once more, since python doesn't have
> symbols, and so the distinction between modules and packages gets
> blurred (in my mind at least): A python modules maps strings directly
> to values without symbols ever entering the discussion.

That's right.  That's why I wrote:

> Modules map symbols/identifiers onto values.

instead of just "modules map symbols onto values."

Lisp uses symbols (and sometimes other things as well) as identifiers. 
Python uses strings.


> I guess what I am saying is that, while packages without symbols don't
> make sense, modules don't require them.  But then, neither did you
> say they do, now that I read what you said over again.

That's mostly right.  At some point you run into the problem of defining
what a symbol is.  In some contexts "symbol" means nothing more than
"uniquified string", in which case Python strings are really symbols:

>>> "foo" is "foo"
1

In Common Lisp symbols have extra stuff attached to them, and the term
"keyword" is sometimes used to refer to a uniqified string without that
extra stuff.  But this usage is far from universal.

E.
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