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Re: adding namespaces to emacs-lisp (better elisp?)

From: Stefan Monnier
Subject: Re: adding namespaces to emacs-lisp (better elisp?)
Date: Fri, 26 Jul 2013 16:59:58 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux)

>> Here's a scenario:
>> - namespaced packages A and B both locally define a function `toto'.
>> - non-namespaced package C comes along with a symbol `toto' somewhere in
>> its code, suddenly causing A and B's `toto' to be global rather
>> than local.
> I don't think this is a serious problem personally. But I'm also not
> wedded to global-obarray-first.

I think it's a very serious problem because it means packages A and
B are at the mercy of some random wholly unrelated package C.

>> Note that instead of "non-namespaced package C", we could have some
>> package which uses symbols as "uniquified strings" and which uses the
>> global obarray for it and might occasionally intern `toto' in the course
>> of its normal execution.
> Again, it only matters if it's a non-namespaced package that does it.

No, a namespaced package can just as easily call `intern'.
But even if you can hope the a namespaced package wouldn't do it, the
non-namespaced packages are very numerous and do all kinds of nasty
stuff and we have very little control over them (e.g. they're not
bundled with Emacs).

>> IOW I think we should instead first look in the local obarray (over
>> which the coder does have control) and if that fails then look in the
>> global obarray.
> I am not wedded to the proposal of using the global obarray first. The
> rules for interning are slightly more complicated in that case:
> - given a string X
> - lookup X in the local obarray
> - if it exists return the symbol
> - else
> -  lookup X in the global obarray
> -  if it exists return the symbol
> -  else
> -    add the symbol to the local obarray

Exactly.  In Mathematica, they have a list of obarrays to check in
sequence and a "current" obarray to which things are added if the
lookup fails.  Sounds clean and simple to me.

> The only problem I see here is the possibility of problems with
> concurrency. The whole operation above would have to be atomic and it
> involves lookups in two separate data structures.

That sounds like a very remote problem to me.  And if/when concurrency
is added it doesn't seem like it should be difficult to make it
work reliably.

> My feeling is that an import should be like the creation of an alias.

Function alias?  Variable alias?
I don't much like the sounds of it.  I'd much rather make sure they are
simply one and the same symbol (I guess "symbol alias").

> It's not that I don't like it per-se. I just want this to be easy to
> implement in the first instance. If the implementation gets more
> difficult later I have no problem with that. But initial low cost is a
> good thing.

I'm not sure why the implementation should be difficult.  `intern' would
"simply" need to parse the string into a list of elements (separated by
"::" or whatever), then lookup the first element in the obarray, which
should contain another obarray, then lookup the second element in that
obarray, etc... until the last element which is handled "in the old

Then (import 'nic as 'foo) would amount to (setq foo nic)


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