Path: utzoo!utgpu!watserv1!watmath!att!rutgers!usc!sdd.hp.com!uakari.primate.wisc.edu!aplcen!aplcomm!uunet!mcsun!ukc!edcastle!aiai!jeff
From: jeff@aiai.ed.ac.uk (Jeff Dalton)
Newsgroups: comp.lang.lisp
Subject: Re: Common Lisp Package System Considered Harmful
Keywords: Packages, CLOS, Object-Oriented Programming, Common Lisp
Message-ID: <3619@skye.ed.ac.uk>
Date: 23 Oct 90 17:13:07 GMT
References: <271E0D40.451E@wilbur.coyote.trw.com> <3596@skye.ed.ac.uk> <272381E7.44AA@wilbur.coyote.trw.com>
Reply-To: jeff@aiai.UUCP (Jeff Dalton)
Organization: AIAI, University of Edinburgh, Scotland
Lines: 77

In article <272381E7.44AA@wilbur.coyote.trw.com> scott@wiley.UUCP (Scott Simpson) writes:
>In article <3596@skye.ed.ac.uk> jeff@aiai.UUCP (Jeff Dalton) writes:
>>So don't use them.  I don't quite understand what you're trying to
>>accomplish.  Are you hoping Common Lisp will change, that the Common
>>Lisp designers will be embarrassed at their incompetence, that Common
>>Lisp will tossed in the trash, or what?
>
>I am trying to get information hiding semantics like Eiffel and Ada in
>Lisp without too much effort. I have been told by many people I
>can't. I believe them. I think you are being a tad touchy here. I
>guess every language news group has its language zealots...

I just think that, after a while, a discussion ought to have some
kind of goal.  At first I thought you were trying to find the best
way to use packages and classes together.  Packages are far from 
perfect, but it makes sense to try to make the best of them.

Later, it seemed that what you wanted was a way to get the same
facilities as Ada or Eiffel.  That too seems reasonable, as far
as it goes.  It turned out that there wasn't a good way to get
such facilities (at least no one has suggested one), but it 
was worth trying.

But then it looked like you'd decided to attack the way Common Lisp
did things, pointing out that it was very unsatisfactory from the
Ada/Eiffel point of view.  Well, fair enough; but at that point it
became less clear what practical result you aimed to accomplish.

I happen to think that different languages are good for different
things and that there isn't much point to "A is better than B"
language wars.  I probably should have written a milder article,
but that's not the way it came out.

There's just no way Common Lisp can satisfy everyone in any case.

>>>Exactly. Strength of will and extraordinary discipline. You hit the
>>>nail on the head. This is *exactly* what I am trying to avoid.
>>>Besides, if we didn't cherish information hiding, language protection
>>>and ease of uses why don't we all go back to programming in assembly
>>>language? They all are Turing machine equivalent anyway. Right? 
>>
>>Turing-equivalence is almost useless as a way to compare programming
>>languages.
>
>This is exactly what I said! I asked a rhetorical question. Reread the
>paragraph starting with "Besides".

As far as I can tell, what you had in mind was either:

 1. If we don't cherish A, B, and C, we may as well use assembler.
 2. People who don't cherish A, B, and C don't understand what
    higher-level languages are for.

>                                   You also edited my paragraph and I
>fear it could be taken out of context. The last sentence of the above
>paragraph stated "We need language features to help in providing
>protection and ease of use."

I edited the quotes to keep down message size.  I didn't ignore the
rest and thought what I kept was representative.  However, if you
think I cut out too much, I accept that and apologize.

Common Lisp has at least two ways to make information relatively
inaccessible.  One is packages.  Packages work fairly well for
some things, but they don't provide the strong inacessibility
that some people want.  The other is lexical scoping.  Lexical
scoping does provide fairly strong inaccessibility, because there
are no facilities in the language for looking inside closures.
So GENERIC-LABELS would let you hide generic functions, in a
sense.

>P.S. I *really* promise not to post after this!

I hope you do post.  Most of what you said about packages was 
well worth reading.

-- Jeff