[Armedbear-devel] Strange behaviour of unexporting and defpackage

[Erik Huelsmann]

Hi Eitaro,

On Sun, Jan 11, 2015 at 6:30 PM, Eitaro Fukamachi <e.arrows at gmail.com>
wrote:

> This is a reproducible script.
>
> ----
> (defpackage unexport-test
>   (:export :a))
>
> (eval-when (:compile-toplevel :load-toplevel :execute)
>   (when (find-package :unexport-test)
>     (do-symbols (symbol :unexport-test)
>       (unexport symbol :unexport-test))))
>
> (defpackage unexport-test
>   (:export :a))
>
> (prin1 (nth-value 1 (intern (string :a) :unexport-test)))
>
>
If cl-colors depends on this behaviour, it's depending on behaviour the cl
spec explicitly named "undefined". From the spec:

If the new definition is at variance with the current state of that
package, the consequences are undefined; an implementation might choose to
modify the existing package to reflect the new definition. (see
http://www.ai.mit.edu/projects/iiip/doc/CommonLISP/HyperSpec/Body/mac_defpackage.html,
third sentence in the Description section)


the important bit is "an implementation *might* choose to modify"; ABCL
currently is an implementation that doesn't modify. Essentially this means
you can - in ABCL's current implementation - just leave out the second
DEFPACKAGE form...

Of course, if you say this is pretty rare when compared to other
implementations, I think we should seriously consider accepting a patch to
change the behaviour. Do you know what the *exact* behaviours of SBCL and
CCL are? Maybe it's not too hard to implement one of the two. Patch
submission always very much welcome as well, of course!


Regards,


-- 
Bye,

Erik.

http://efficito.com -- Hosted accounting and ERP.
Robust and Flexible. No vendor lock-in.
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